COMPONENTS OF AN ENERGY EFFICIENT BUILDING
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COMPONENTS OF AN ENERGY EFFICIENT BUILDING
Green Buildings and Energy Efficient Buildings
Green building (also known as green construction or sustainable building) is the practice of creating structures and using processes that are environmentally responsible and resourceefficient throughout a building's life-cycle: from siting to design, construction, operation, maintenance, renovation, and demolition. This practice expands and complements the classical building design concerns of economy, utility, durability, and comfort. Although new technologies are constantly being developed to complement current practices in creating greener structures, the common objective is that green buildings are designed to reduce the overall impact of the built environment on human health and the natural environment by:
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Efficiently using energy, water, and other resources Protecting occupant health and improving employee productivity Reducing waste, pollution and environmental degradation
Some of the major components and devices used in an energy efficient building are as follows • Energy Recovery Ventilator • Heat Recovery Ventilation • Radiant Flooring - Under Floor Heating • Structural Insulated Panels • Photovoltaic Array • Heat Pumps • North Wall • Clerestory lightings and Skylight • Attached Greenhouses • Roof Ponds
Energy Recovery Ventilator (ERV)
Introduction An Energy Recovery Ventilator (ERV) is a mechanical device that draws stale air from the house and transfers the heat or coolness in that air, to the air being pulled into the house. This can help reduce energy costs and dilute indoor pollutants. It is a type of air-to-air heat exchanger that not only can transfer sensible heat but also latent heat. Since both temperature and moisture is transferred, ERVs can be considered total enthalpic devices
Energy Recovery Ventilation
Introduction Energy Recovery Ventilation (ERV) is the energy recovery process of exchanging the energy contained in normally exhausted building or space air and using it to treat, precondition, the incoming outdoor ventilation air in residential and commercial HVAC systems. During the warmer seasons the system will pre-cool and dehumidify while humidifying and pre-heating in the cooler seasons. This system will allow for the indoor environment to maintain a relative humidity of an appealing 40% to 50% range. This range can be maintained under essentially all conditions. The only energy penalty is the power needed for the blower to overcome the pressure drop in the system. Brief Description ERVs are especially recommended in climates where cooling loads place strong demands on HVAC
(heating, ventilation and air-conditioning) systems. However, keep in mind that ERVs are not dehumidifiers. They transfer moisture from the humid air stream (incoming outdoor air in the summer) to the exhaust air stream. But, the desiccant wheels used in many ERVs become saturated fairly quickly and the moisture transfer mechanism becomes less effective with successive hot, humid periods. In some cases, ERVs may be suitable in climates with very cold winters. If indoor relative humidity tends to be too low, what available moisture there is in the indoor exhaust air stream, is transferred to incoming outdoor air. ERVs also allow the exchange of moisture to control humidity. This can be especially valuable in situations where problems may be created by extreme differences in interior and exterior moisture levels. For instance in cold, heating-dominated climates, better air flow and the introduction of humidity to the indoor environment can help control wintertime window condensation. In humid summer climates which are cooling dominated, it can be critical to dry out incoming air so that mildew or mold does not develop in ductwork. Methods of Transfer Throughout the cooling season, the system works to cool and dehumidify the incoming, outside air. This is accomplished by the system simply taking the rejected heat and sending it into the exhaust airstream. Sequentially, this air cools the condenser coil at a lower temperature than if the rejected heat
had not entered the exhaust airstream. During the heating seasons, the system works in reverse. Instead of discharging the heat into the exhaust airstream, the system draws heat from the exhaust airstream in order to pre-heat the incoming air. At this stage, the air passes through a primary unit and then into a space. With this type of system, it is normal, during the cooling seasons, for the exhaust air to be cooler than the ventilation air and, during the heating seasons, warmer than the ventilation air. It is this reason the system works very efficiently and effectively. The Coefficient of Performance (COP) will increase as the conditions become more extreme (i.e., more hot and humid for cooling and colder for heating).[4] Efficiency The efficiency of an ERV system is the ratio of energy transferred between the two air streams compared with the total energy transported through the heat exchanger.[5][6] Types of Energy Recovery Devices Energy Recovery Devices Rotary Enthalpy Wheel Fixed Plate Heat Pipe Run Around Loop Type of Transfer Total & Sensible Total** & Sensible Sensible Sensible
Thermo-siphon Twin Towers
Sensible Sensible
**Total Energy Exchange only available on Hygroscopic units and Condensate Return units Rotary Air-to-Air Enthalpy Wheel The rotating wheel heat exchanger is composed of a rotating cylinder filled with an air permeable material resulting in a large surface area. The surface area is the medium for the sensible energy transfer. As the wheel rotates between the ventilation and exhaust air streams it picks up heat energy and releases it into the colder air stream. The driving force behind the exchange is the difference in temperatures between the opposing air streams which is also called the thermal gradient. Typical media used consists of polymer, aluminum, and synthetic fiber. The Enthalpy Exchange is accomplished through the use of desiccants. Desiccants transfer moisture through the process of adsorption which is predominately driven by the difference in the partial pressure of vapor within the opposing air-streams. Typical desiccants consist of Silica Gel, and molecular sieves. Though very effective in its energy recovery, rotary enthalpy wheels have the common characteristic of high static pressures and poor durability. Therefore they are not as practical for energy savings purposes, and should only be considered for a cheaper alternative - in comparison to other ERVs for situations where increased fresh outdoor
ventilation is required. High static pressures result in increased fan power lowering the net energy savings of an installation. As for durability, rotary enthalpy wheels are normally guaranteed for no longer than 1 year, and the characteristic lifetime is about 5 years.
Plate Heat Exchanger Fixed plate heat exchangers have no moving parts. Plates consist of alternating layers of plates that are separated and sealed. Typical flow is cross current and since the majority of plates are solid and non permeable, sensible only transfer is the result. The tempering of incoming fresh air is done by a heat or energy recovery core. In this case, the core is made of aluminum or plastic plates. Humidity levels are adjusted through the transferring of water vapor. This is done with a rotating wheel either containing a desiccant material or permeable plates.[11]The percentage of the total energy saved will depend on the efficiency of the device (up to 90%) and the latitude of the building
Heat Pipe Exchanger A heat pipe is a passive energy recovery heat exchanger that has the appearance of a common plate-finned water coil except the tubes are not interconnected. Additionally it is divided into two sections by a sealed partition. Hot air passes through one side (evaporator) and is cooled while cooler air passes through the other side (condenser). While heat pipes are sensible heat transfer exchangers, if the air conditions are such that condensation forms on the fins there can be some latent heat transfer and improved efficiency.
Heat pipes are tubes that have a capillary wick inside running the length of the tube, are evacuated and then filled with a refrigerant as the working fluid, and are permanently sealed. The working fluid is selected to meet the desired temperature conditions and is usually a Class I refrigerant. Fins are similar to conventional coils - corrugated plate, plain plate, spiral design. Tube and fin spacing are selected for appropriate pressure drop at design face velocity. HVAC systems typically use copper heat pipes with aluminum fins; other materials are available.
Run-around Loop Systems The run-around heat recovery system is a simple piping loop, containing a circulator; the loop connects a finned-tube coil in the exhaust plenum with a finned-tube coil in the make-up air plenum or AHU. The coils are connected in a closed loop via counterflow piping through which an intermediate heat transfer fluid (typically water or a freezepreventive solution) is pumped. The warm exhaust air heats the circulating fluid; this fluid then warms the cool make-up air. The heat recovery system typically operates to preheat outdoor make-up air but also to pre-cool the make-up air when the exhaust air stream is cooler than the outdoor makeup air. This system operates for sensible heat recovery only. In comfort-to-comfort applications, energy transfer is seasonally reversible—the supply air is preheated when the outdoor air is cooler than the exhaust air and precooled when the outdoor air is warmer.
Thermo-Siphon Thermosiphon refers to a method of passive heat exchange based on natural convection which circulates liquid without the necessity of a mechanical pump. This circulation can either be open-loop, as when liquid in a holding tank is passed in one direction via a heated transfer tube mounted at the bottom of the tank to a distribution point even one mounted above the originating tank - or it can be a vertical closed-loop circuit with return to the original vessel. Its intended purpose is to simplify the pumping of liquid and/or heat transfer, by avoiding the cost and complexity of a conventional liquid pump. Solar Energy
Thermosiphons are used in some liquid-based solar heating systems to heat a liquid such as water. The water is heated passively by solar energy and relies on heat energy being transferred from the sun to a solar collector. The heat from the collector can be transferred to water in two ways: directly where water circulates through the collector, or indirectly where an anti-freeze solution carries the heat from the collector and transfers it to water in the tank via a heat exchanger. Convection allows for the movement of the heated liquid out of the solar collector to be replaced by colder liquid which is in turn heated. Due to this principle, it is necessary for the water to be stored in a tank above the collector.
Heat Recovery Ventilation
Introduction
Heat recovery ventilation, also known as HRV, Mechanical ventilation heat recovery, or MVHR, is an energy recovery ventilation system, using equipment known as a heat recovery ventilator, Heat exchanger, air exchanger or air-to-air exchanger, that employs a counter-flow heat exchanger (countercurrent heat exchange) between the inbound and outbound air flow. HRV provides fresh air and improved climate control, while also saving energy by reducing the heating (or cooling) requirements. Incoming Air The air coming into the heat exchanger should be at least 0°C. Otherwise humidity in the outgoing air may condense, freeze and block the heat exchanger. A high enough incoming air temperature can also be achieved by
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recirculating some of the exhaust air (causing loss of air quality) when required, by using a very small (1 kW) heat pump to warm the inlet air above freezing before it enters the HRV. (The 'cold' side of this heatpump is situated in the warm air outlet.)
Air to Air Heat Exchanger There are a number of heat exchangers used in Heat recovery ventilation-HRV devices, as diagrammed to the right :
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cross flow heat exchanger up to 60% efficient (passive) countercurrent heat exchanger up to 99% efficient (passive) rotary heat exchanger (requires motor to turn wheel) heat pipes thin multiple heat wires (Fine wire heat exchanger)
Earth-to-Air Heat Exchanger
This can be done by an earth warming pipe ("groundcoupled heat exchanger"), usually about 30 m to 40 m long and 20 cm in diameter, typically buried about 1.5 m below ground level In high humidity areas where internal condensation could lead to fungal / mould growth in the tube leading to contamination of the air, several measures exist to prevent this.
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Ensuring the tube drains of water. Regular cleaning Tubes with an imbedded bactericide coating such as silver ions (non-toxic for humans) Air filters F7 / EU7 (>0,4 micrometres) to traps mould (of a size between 2 & 20 micrometres). UV air purification Use a earth to "water" heat exchanger.The pipes may be either corrugated/slotted to enhance heat transfer and provide condensate drainage or smooth/solid to prevent gas/liquid transfer.
Earth-to-Water Heat Exchanger
An alternative to the earth to air heat exchanger is the earth to "water" heat exchanger. This is typically similar to a geothermal heat pump tubing embedded horizontally in the soil (or could be a vertical pipe/sonde) to a similar depth of the EAHX. It uses approximately double the length of pipe Ø 35 mm ie around 80 metres compared to an EAHX. A heat exchanger coil is placed before the air inlet of the HRV. Typically a brine liquid (heavily salted water) is used as the heat exchange fluid which is slightly more efficient and environmentally friendly than polypropylene heat transfer liquids. In temperate climates in an energy efficient building, this is more than sufficient for comfort cooling during summer without resorting to an airconditioning system. In more extreme hot climates a very small air to air micro-heat pump in reverse (an air conditioner) with the evaporator (giving heat) on the air inlet after the HRV heat exchanger and the condensor (taking heat) from the air outlet after the heat exchanger will suffice.
Radiant Heating
Introduction Radiant heating is a technology for heating indoor and outdoor areas. Radiant heating consists of radiant energy being emitted from a heat source. Radiant heating heats a building through radiant heat, rather than other conventional methods including convection heating. The heat energy is emitted from a warm element, such as a floor, wall or overhead panel, and warms people and other objects
in rooms rather than directly heating the air. The internal air temperature for radiant heated buildings may be lower than for a conventionally heated building to achieve the same level of body comfort, when adjusted so the perceived temperature is actually the same. In the case of heating outdoor areas, the surrounding air is constantly moving, making conventional patio heaters, also known as "mushroom heaters", which rely partly on convection heating, impractical. The reason being, that once you heat the outside air, it will blow away with air movement. Outdoor radiant heaters allow specific spaces within an outdoor area to be targeted, warming only the people and objects in their path. The radiant heating systems can be divided into:
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Underfloor heating systems—electric or hydronic Wall heating systems Radiant ceiling (overhead) panels Trace heating- Gutter and Roof De-icing Snowmelt system- Electric or Hydronic Overhead natural gas-fired radiant heaters
Underfloor Heating Underfloor heating and cooling is a form of central heating and cooling which achieves indoor climate control for thermal comfort using conduction, radiation and convection. Description
Modern underfloor heating systems use either electrical resistance elements ("electric systems") or fluid flowing in pipes ("hydronic systems”) to heat the floor. Either type can be installed as the primary, whole-building heating system or as localized floor heating for thermal comfort. Electrical resistance can only be used for heating so when space cooling is also required, hydronic systems are used. Electric heating elements or hydronic piping can be cast in a concrete floor slab ("poured floor system" or "wet system"). They can also be placed under the floor covering ("dry system") or attached directly to a wood sub floor ("sub floor system" or "dry system").
Hydronic Systems
Hydronic systems use water or a mix of water and anti-freeze such as propylene glycol as the heat transfer fluid in a "closed loop" that is recirculated between the floor and the boiler. Various types of pipes are available specifically for hydronic underfloor heating and cooling systems and are generally made from polyethylene including PEX, PEX-Al-PEX and PERT. Older materials such as Polybutylene (PB) and copper or steel pipe are still used in some locales or for specialized applications. Hydronic systems require skilled designers and tradespeople familiar with boilers, circulators, controls, fluid pressures and temperature. The use of modern factory assembled sub-stations, used primarily in district heating and cooling, can greatly simplify design requirements and reduce the installation and commissioning time of hydronic systems. Hydronic systems can use a single source or combination of energy sources to help manage energy costs. Hydronic system energy source options are:
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Boilers (heaters) including Combined heat and power plants heated by:
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Natural gas, coal, oil or waste oil Electricity Solar thermal wood or other biomass bio-fuels
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Heat pumps and chillers powered by:
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Electricity Natural gas
Electric systems
Electric systems are used only for heating and employ noncorrosive, flexible heating elements including cables, pre-formed cable mats, bronze mesh, and carbon films. Due to their low profile they can be installed in a thermal mass or directly under floor finishes. Electric systems can also take advantage of time-of-use electricity metering and are frequently used as carpet heaters, portable under area rug heaters, under laminate floor heaters, under tile heating, under wood floor heating, and floor warming systems, including under shower floor and seat heating. Large electric systems also require skilled designers and tradespeople but this is less so for small floor warming systems. Electric systems use
fewer components and are simpler to install and commission than hydronic systems. Some electric systems use line voltage technology while others use low voltage technology. Power consumption of an electric system is not based on voltage but rather wattage output produced by the heating element.
Indoor Air
Quality
Underfloor heating can have a positive effect on the quality of indoor air by facilitating the choice of otherwise perceived cold flooring materials such as tile, slate, terrazzo and concrete. These masonry surfaces typically have very low VOC emissions (volatile organic compounds) in comparison to other flooring options. In conjunction with moisture control, floor heating also establishes temperature conditions that are less favorable in supporting mold, bacteria, viruses and dust mites. By removing the sensible heating load from the total HVAC (Heating, Ventilating, and Air Conditioning) load, ventilation, filtration and dehumidification of incoming air can be accomplished with dedicated outdoor air systems having less volumetric turnover to mitigate distribution of airborne contaminates. There is recognition from the medical community relating to
the benefits of floor heating especially as it relates to allergens. Typical Installation Details
General considerations for placing radiant heating and cooling pipes in flooring assemblies where other HVAC and plumbing components may be present.
Technical Design The amount of heat exchanged from or to an underfloor system is based on the combined radiant and convective heat transfer coefficients.
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Radiant heat transfer is constant based on the Stefan–Boltzmann constant. Convective heat transfer changes over time depending on o the air's density and thus its buoyancy. Air buoyancy changes according to surface temperatures and o forced air movement due to fans and the motion of people and objects in the space.
Convective heat transfer with underfloor systems is much greater when the system is operating in a heating rather than cooling mode. Typically with underfloor heating the convective component is almost 50% of the total heat transfer and in underfloor cooling the convective component is less than 10%. Sample - Mechanical Schematic Representation
Illustrated is a simplified mechanical schematic of an underfloor heating and cooling system for thermal comfort quality with a separate air handling system for indoor air quality. In high performance residential homes of moderate size (e.g. under 2 2 3000 ft (278 m ) total conditioned floor area), this system using manufactured hydronic control appliances would take up about the same space as a three or four piece bathroom.
Structural Insulated Panels
Structural insulated panels, SIPs, are a composite building material. They consist of an insulating layer of rigid polymer foam sandwiched between two layers of structural board. The board can be sheet metal, plywood, cement or oriented strand board
(OSB) and the foam either expanded polystyrene foam (EPS), extruded polystyrene foam (XPS) or polyurethane foam. SIPs share the same structural properties as an Ibeam or I-column. The rigid insulation core of the SIP acts as a web, while the OSB sheathing exhibits the same properties as the flanges. SIPs combine several components of conventional building, such as studs and joists, insulation, vapor barrier and air barrier. They can be used for many different applications, such as exterior wall, roof, floor and foundation systems.
Materials SIPs are most commonly made of OSB panels sandwiched around a foam core made of expanded polystyrene (EPS), extruded polystyrene (XPS) or rigid polyurethane foam, but other materials can be
used, such as plywood, pressure-treated plywood for below-grade foundation walls, steel, aluminum, cement board such as Hardibacker, and even exotic materials like stainless steel, fiber-reinforced plastic, and magnesium oxide. Some SIPs use fiber-cement or plywood sheets for the panels, and agricultural fiber, such as wheat straw, for the core. The third component in SIPs is the spline or connector piece between SIP panels. Dimensional
lumber is commonly used but creates thermal bridging and lowers insulation values. To maintain higher insulation values through the spline manufacturers use Insulated Lumber, Composite Splines, Mechanical Locks, Overlapping OSB Panels, or other creative methods. Depending on the method selected other advantages such as full nailing surfaces or increased structural strength may become available. Slab Energy Loss Even if the foundation walls under the slab are insulated, that will not help much if the slab edge close the outside air isn’t also insulated. Slab Insulation Slab insulation uses a rigid insulation material: typically foam boards. The installation is easy: just apply the right product with the right r-value under the face of the slab.
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As the figures show, a well done slab insulation also comprises perimeter insulation, that is, insulation of the slab edge closer to the outside air. Slab Insulation Depth and R-values
The depth and the R-value recommended when insulating a slab varies with climate zones. More exactly they vary with the Heating Degree Days (HDD) of your particular climate zone. The HDD is an index reflecting the energy needs to heat or cool a home. If your climate zone has a HDD of zero that means that you do not need to insulate your slab. That happens whenever the difference between 65ºF/18ºC and the average outside temperature is very close to zero during the whole year (outside 65ºF/18ºC - «the base temperature» - is the temperature that technicians consider the ideal to get a comfortable indoor temperature; with that outside temperature, the occupants and the home appliances will add more heat to indoor home temperatures, making them comfortable). The higher the difference between the outside temperature and the 65ºF/18ºC, the higher the HDD and the needs of insulation; the higher the number of days with a high HDD, the higher the needs of insulation. The table below shows recommended R-values and slab insulation depth by the official Energy Conservation Code Council (IECC) . Recommended R-Values and Depth for Slab Insulation Heating Feet/cm Degree Installed Days Verticall (HDD) y R-Value
0 to 2,499 2,499 to 4,500 4,500 to 6,000 6,000 to 7,200 7,200 to 8,700 8,700 to 10,000 10,000 to 12,400 12,400 to 14,000
none required 2 feet/6 cm 4 feet/12 cm 4 feet/12 cm 4 feet/12 cm 4 feet/12 cm 4 feet/12 cm 4 feet/12 cm
none required R-4 R-5 R-6 R-7 R-8 R-9 R-10
Insulation of the Outside or the Inside Foundation Wall The insulation may be applied outside or inside the foundation wall. You should also apply a good finish protection (metal flashing, is a common option) and a protective termite shield (also advisable in the insulation involving the inside foundation wall).
Insulation Slab Techniques Slab insulation can be installed using foam board rigid insulation directly against the footing and the exterior of the slab, as shown in the images above.Alternatively, when building the slab you can also build "contained”/"floating" slab with interior insulation. The material is typically the same: board rigid insulation.
Photovoltaic Array
A photovoltaic array (also called a solar array) is a linked collection of photovoltaic modules, which are in turn made of multiple interconnected solar cells. The cells convert solar energy into direct current electricity via the photovoltaic effect. The power that one module can produce is seldom enough to meet requirements of a home or a business, so the modules are linked together to form an array. Most PV arrays use an inverter to convert the DC power produced by the modules into alternating current that can plug into the existing infrastructure to power lights, motors, and other loads. The modules in a PV array are usually first connected in series to obtain the desired voltage; the individual strings are then connected in parallel to allow the system to produce more current. Solar arrays are typically measured by
the peak electrical power they produce, in watts, kilowatts, or even megawatts. A photovoltaic array is a linked system of photovoltaic (PV) modules. The solar cells in the PV modules convert sunlight into electricity by bouncing the sun's photons off of silicon solar cells which produce current through the photoelectric effect. Most PV systems utilize an "inverter" to convert DC power produced by the modules to alternating current (AC) that can be used to power appliances. The solar cells are usually connected in series on the panel to achieve the desired voltage. Each individual string thereafter is connected in parallel to produce more current. Tracking systems and sensors are also placed on many solar arrays to increase the output. In some cases the increase in viable output has been up to 100%. Large scale photovoltaic arrays producing more than 1MW of electricity use solar trackers to optimize the amount of sunlight it collects. Solar collectors are another way to optimize the sunlight reaching the PV array. Solar collectors concentrate sunlight through the use of mirrors and reflective surfaces in a cost efficient way to increase the output in PV arrays. Uninsulated slabs are a cause of heating losses and uncomfortable floors and energy-inefficiency.
Heat Pumps
Air-source heat pumps (ASHP) can be thought of as reversible air conditioners. Like an air conditioner, an ASHP can take heat from a relatively cool space (e.g. a house at 70°F) and dump it into a hot place (e.g. outside at 85°F). However, unlike an air conditioner, the condenser and evaporator of an ASHP can switch roles and absorb heat from the cool outside air and dump it into a warm house. Air-source heat pumps are inexpensive relative to other heat pump systems. However, the efficiency of air-source heat pumps decline when the outdoor temperature is very cold or very hot; therefore, they are only really applicable in temperate climates. For areas not located in temperate climates, groundsource (or geothermal) heat pumps provide an efficient alternative. The difference between the two
heat pumps is that the ground-source has one of its heat exchangers placed underground—usually in a horizontal or vertical arrangement. Ground-source takes advantage of the relatively constant, mild temperatures underground, which means their efficiencies can be much greater than that of an airsource heat pump. The in-ground heat exchanger generally needs a considerable amount of area. Designers have placed them in an open area next to the building or underneath a parking lot. In terms of initial cost, the ground-source heat pump system costs about twice as much as a standard airsource heat pump to be installed. However, the upfront costs can be more than offset by the decrease in energy costs. The reduction in energy costs is especially apparent in areas with typically hot summers and cold winters. Other types of heat pumps are water-source and airearth. If the building is located near a body of water, the pond or lake could be used as a heat source or sink. Air-earth heat pumps circulate the building’s air through underground ducts. With higher fan power requirements and inefficient heat transfer, Air-earth heat pumps are generally not practical for major construction
North Walls
In an east-west oriented building, a north facing exterior wall will receive little sunlight during the winter and this will be a major source of heat loss since heat always moves toward cold. Additionally, building shading of north side open space usually renders it unusable for outdoor use. To alleviate these situations the building should be shaped so that the roof slopes downward from the south to the north wall. This reduces the height of the north face of the building and therefore the area through which
heat is lost. This also allows sunlight to reach more area of north side outdoor spaces. Variations of reducing heat loss conditions manifest in north walls include backing the building into a sloped hillside or providing a berm, both of which reduce the exposed north area.
South to north downward sloping roof reduces heat loss from the north wall and allows sunlight to reach north side open space.
Clerestories and Skylights
Many conditions make south wall heat collection for direct gain problematic, but it can be easily mitigated by the use of clerestories or skylights. Both of these features admit sunlight at the roof structure of a building and can be used to direct sunlight to a specific interior surface. They can also be used in combination with or as a supplement to a south facing glazed wall. Additionally, they provide for natural light applications, which can reduce the need and cost of artificial lighting. Clerestories are vertical south facing windows located at roof level ,Their advantages are that they
allow diffuse lighting into a room; they provide privacy; and they can be placed almost anywhere on a roof. In a compartmentalized building layout, each room can have its own source of heat and light. They should be located at a distance from a thermal storage wall that allows direct sunlight to hit the wall throughout the winter. This distance is roughly 1.5 times the height of the wall. Ceilings in rooms containing clerestories should be light in color to reflect or diffuse sunlight into the living space. Large interior spaces may have multiple clerestories arranged to allow maximum admission of sunlight. Care must be taken that they do not shade each other, so the clerestorey roof angle (from horizontal) of each clerestorey should be roughly the same angle of the sun at its lowest winter point (noon on December 21). Skylights are simply openings in a roof, which admit sunlight -they are either horizontal (a flat roof) or pitched at the same angle as the roof slope. In most cases. horizontal skylights are used with reflectors to increase the intensity of solar radiation (remember the angle of incidence). Large skylights should be provided with shading devices to prevent heat loss at night and heat gain during the summer months
Clerestory clerestories can be used to provide sunshine onto interior walls which would normally not have a clear view of winter sunlight.
. Skylights provide an alternative for direct solar gain, shading devices must be included as an integral part of the skylight to prevent overheating the space during mild periods.
Attached Green Houses
An indirect gain heating system, using a green house structure as a heat collector, is multi-purpose, practical and efficient. It also requires the most rigorous design because of its multiple nature, which affects sizing for space heating, creating ideal conditions for greenhouse conditions, and accurately predicting performance for both. The attachment of a greenhouse to the south side of a building enables the structure to benefit from the normal, heat collecting greenhouse operation. The greenhouse collects heat due to its solar exposure. This heat can be conducted through a thermal storage wall separating house and greenhouse, or can be convected to the interior space of the building. In this way the greenhouse serves both as a heat collector, and a solarium for people and plants. Generally, in cold climates, a greenhouse design would use between 0.65 and 1.5 square feet of south facing double glass greenhouse collecting surface for each square foot of floor area in the adjacent living space. In more moderate climates this can be reduced to
0.33 and 0.9 square feet. This should provide enough heat to keep the average temperature in the adjacent space between 60°F and 70°F.
It is desirable for a solar greenhouse structure to be recessed into the south facade of the building, thereby minimizing east and west exposures, which have little effect on heat collection but can be a great source of heat loss. Furthermore, heat transfer through the common wall between the greenhouse and the living space is increased in this configuration Greenhouses for heating purposes can be added to frame buildings to provide for direct heat during winter days, but such buildings, without thermal storage mass, do not have the ability nor capacity to store heat for use at night. Some designs integrating greenhouses, adjust for nighttime heating by transfer of all greenhouse heat to main building storage mass (floors, walls, etc.) for deferred use at night. This only works in moderately cold climates, because very cold climates require the residual heat collected by the
greenhouse to keep it, and its contents, from freezing at night. The common wall between the greenhouse and the building interior can be constructed of thermal mass materials (masonry, water, etc.). The greenhouse side of common walls should be dark in color (better absorber) and should receive maximum sunlight throughout the day. Wall vents and/or operable windows can be used to allow heated air directly into the interior space during the daytime. Wall thickness should be same as that provided for in an indirect gain (Trombe) wall. If water is used, its minimum thickness should be 8 inches (or 0.67 cubic feet for each square foot of south-facing glass). Masonry walls cannot absorb and transfer heat as fast as a greenhouse can collect it. As a result, temperatures in the greenhouse will fluctuate as much as 60°F on a clear day. To dampen (level out) these fluctuations, extra storage mass (such as masonry units or containers filled with water) can be placed in the greenhouse. These act as an interior heat dampening water wall (1 cubic foot of water for each square foot of south facing glass will reduce temperature fluctuations 25°F to 29°F). If water is used as the common wall between the greenhouse and the living space, temperature fluctuations will be smaller, and if more than the 0.67 cubic feet of water for each square foot of glass is used in the wall, temperature fluctuations will be further reduced.
In cold climates, it may be advantageous to utilize a heat storage, in the form of a rock bin, under the building or living space, which would act as thermal storage of heat collected during the day. Heat transfer can occur by natural convection if the building is terraced up a slope, or by use of a fan, which would transfer heat to a rock bed located in a crawl space under the floor of the structure The rock bed should spread across 75 to 100% of the floor area of the structure in cold climates, and 50 to 75% of the floor area in moderate climates. Heat from the greenhouse should be directed over the rock bed and a means of returning cold air from the bottom of the rock bed to the greenhouse should be provided. If a terraced design is used, colder air will naturally settle due to the convective loop cycle. About 1.5 to 3 cubic feet of fist-sized rock is necessary in cold climates and .5 to 1 cubic feet in temperate climates. Rock bin storage has also been used as a part of a cooling system in warmer climes.
By extending the end walls of an attached greenhouse, loss to the outside is reduced while the heat gains to the space are incresed.
Small fans (less than 0.25 H.P.) can be used to aid in the transfer of heat from collection space to more remote parts of the structure.
Roof Ponds
Roof ponds can be used both for heating during the winter months and for cooling during the summer months. For latitudes higher that 36° north, roof ponds require greater solar gain exposure as well as greater protection from loss of gained heat.
The system is simple in concept. The roof pond approach brings the differing building aspects of a building - roof, ceiling, heating (and cooling) system, and heat distribution (does away with ducts) into one system. The roof ponds of contained water are the heating (and cooling) unit. The roof/ceilings of the building act as the structural support for the roof ponds; the "radiator" device for evenly distributed heating of the spaces below; and as a waterproof roof system providing protection from the elements.
The movable insulation above the ponds is the weather protection, heating/cooling system "manager" and additional protection from the elements. Wintertime heating is comprised of daytime opening the insulating roof layer to allow solar radiation to heat the water beds; water bed warming heats the supporting structure which is also the ceiling for spaces below; heated support structure radiates heat to the space. At night the insulated roof panels close to contain heat gathered by the ponds to continue heating the spaces below. The sun in northern latitudes is at a lower angle with solar radiation traveling through a greater mass of atmosphere, which reduces its energy content by scattering and reflection. In this situation, increased area of exposure or use of solar reflection can be used to increase roof pond effectiveness. Additionally, in colder climates, the roof pond system benefits from insulating covers to prevent nighttime losses. The most beneficial insulation system is one that is multi-purpose and movable, operating only twice a day to 1) expose the ponds for heat collection, and 2) to cover the ponds to prevent heat loss at night. This insulation system is also beneficial in the summer when the roof ponds must be insulated to prevent summer heat gain. The movable insulation structure can operate in a number of ways - rolling, hinged, etc.. In climates where snow is likely, ponds can be placed in a solar attic below the sloping roof with south facing glazing to allow solar gain, and the attic ceiling can be painted o a reflective color or sheathed with a reflective material. To increase system performance, glazing for cold
climate solar ponds can be dual pane, or the ponds can contain an upper layer inflated air cell. It is important to provide a waterproof layer (membrane, etc.) at the pond support system surface to provide protections during draining of water for maintenance, and from water bed material failure and/or weather impacts. The capability to drain the ponds in an easy and non-damaging manner is important. The water should be enclosed in ultraviolet light inhibiting (prevents degradation) plastic bags, waterproof structural metal or fiberglass tanks which form the ceiling below. The top of the water containment system must be transparent and the sides/bottom a dark color. Insulation panels should be constructed so that they can be tightly sealed when closed to prevent infiltration heat loss. In some applications insulating panels can also serve as reflectors when open in order to direct more solar to the ponds.
Heat is transferred from the roof ponds through the support deck to the interior space below. The edges of the deck should be carefully insulated to reduce heat loss. The underside of the support deck serves as an interior ceiling, and all surfaces (including galvanized metal decking) should be painted. Because the system provides a "radiant" ceiling it is important that no insulation is used between the root
pond and the interior space. The one exception to this rule is at the bathroom, which generates high humidity from showers and tubs. Here, an
uninsulated ceiling can result in condensation and drippage, so effective water barriers and insulation are critical.
Green Buildings and Energy Efficient Buildings
Green building (also known as green construction or sustainable building) is the practice of creating structures and using processes that are environmentally responsible and resourceefficient throughout a building's life-cycle: from siting to design, construction, operation, maintenance, renovation, and demolition. This practice expands and complements the classical building design concerns of economy, utility, durability, and comfort. Although new technologies are constantly being developed to complement current practices in creating greener structures, the common objective is that green buildings are designed to reduce the overall impact of the built environment on human health and the natural environment by:
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Efficiently using energy, water, and other resources Protecting occupant health and improving employee productivity Reducing waste, pollution and environmental degradation
Some of the major components and devices used in an energy efficient building are as follows • Energy Recovery Ventilator • Heat Recovery Ventilation • Radiant Flooring - Under Floor Heating • Structural Insulated Panels • Photovoltaic Array • Heat Pumps • North Wall • Clerestory lightings and Skylight • Attached Greenhouses • Roof Ponds
Energy Recovery Ventilator (ERV)
Introduction An Energy Recovery Ventilator (ERV) is a mechanical device that draws stale air from the house and transfers the heat or coolness in that air, to the air being pulled into the house. This can help reduce energy costs and dilute indoor pollutants. It is a type of air-to-air heat exchanger that not only can transfer sensible heat but also latent heat. Since both temperature and moisture is transferred, ERVs can be considered total enthalpic devices
Energy Recovery Ventilation
Introduction Energy Recovery Ventilation (ERV) is the energy recovery process of exchanging the energy contained in normally exhausted building or space air and using it to treat, precondition, the incoming outdoor ventilation air in residential and commercial HVAC systems. During the warmer seasons the system will pre-cool and dehumidify while humidifying and pre-heating in the cooler seasons. This system will allow for the indoor environment to maintain a relative humidity of an appealing 40% to 50% range. This range can be maintained under essentially all conditions. The only energy penalty is the power needed for the blower to overcome the pressure drop in the system. Brief Description ERVs are especially recommended in climates where cooling loads place strong demands on HVAC
(heating, ventilation and air-conditioning) systems. However, keep in mind that ERVs are not dehumidifiers. They transfer moisture from the humid air stream (incoming outdoor air in the summer) to the exhaust air stream. But, the desiccant wheels used in many ERVs become saturated fairly quickly and the moisture transfer mechanism becomes less effective with successive hot, humid periods. In some cases, ERVs may be suitable in climates with very cold winters. If indoor relative humidity tends to be too low, what available moisture there is in the indoor exhaust air stream, is transferred to incoming outdoor air. ERVs also allow the exchange of moisture to control humidity. This can be especially valuable in situations where problems may be created by extreme differences in interior and exterior moisture levels. For instance in cold, heating-dominated climates, better air flow and the introduction of humidity to the indoor environment can help control wintertime window condensation. In humid summer climates which are cooling dominated, it can be critical to dry out incoming air so that mildew or mold does not develop in ductwork. Methods of Transfer Throughout the cooling season, the system works to cool and dehumidify the incoming, outside air. This is accomplished by the system simply taking the rejected heat and sending it into the exhaust airstream. Sequentially, this air cools the condenser coil at a lower temperature than if the rejected heat
had not entered the exhaust airstream. During the heating seasons, the system works in reverse. Instead of discharging the heat into the exhaust airstream, the system draws heat from the exhaust airstream in order to pre-heat the incoming air. At this stage, the air passes through a primary unit and then into a space. With this type of system, it is normal, during the cooling seasons, for the exhaust air to be cooler than the ventilation air and, during the heating seasons, warmer than the ventilation air. It is this reason the system works very efficiently and effectively. The Coefficient of Performance (COP) will increase as the conditions become more extreme (i.e., more hot and humid for cooling and colder for heating).[4] Efficiency The efficiency of an ERV system is the ratio of energy transferred between the two air streams compared with the total energy transported through the heat exchanger.[5][6] Types of Energy Recovery Devices Energy Recovery Devices Rotary Enthalpy Wheel Fixed Plate Heat Pipe Run Around Loop Type of Transfer Total & Sensible Total** & Sensible Sensible Sensible
Thermo-siphon Twin Towers
Sensible Sensible
**Total Energy Exchange only available on Hygroscopic units and Condensate Return units Rotary Air-to-Air Enthalpy Wheel The rotating wheel heat exchanger is composed of a rotating cylinder filled with an air permeable material resulting in a large surface area. The surface area is the medium for the sensible energy transfer. As the wheel rotates between the ventilation and exhaust air streams it picks up heat energy and releases it into the colder air stream. The driving force behind the exchange is the difference in temperatures between the opposing air streams which is also called the thermal gradient. Typical media used consists of polymer, aluminum, and synthetic fiber. The Enthalpy Exchange is accomplished through the use of desiccants. Desiccants transfer moisture through the process of adsorption which is predominately driven by the difference in the partial pressure of vapor within the opposing air-streams. Typical desiccants consist of Silica Gel, and molecular sieves. Though very effective in its energy recovery, rotary enthalpy wheels have the common characteristic of high static pressures and poor durability. Therefore they are not as practical for energy savings purposes, and should only be considered for a cheaper alternative - in comparison to other ERVs for situations where increased fresh outdoor
ventilation is required. High static pressures result in increased fan power lowering the net energy savings of an installation. As for durability, rotary enthalpy wheels are normally guaranteed for no longer than 1 year, and the characteristic lifetime is about 5 years.
Plate Heat Exchanger Fixed plate heat exchangers have no moving parts. Plates consist of alternating layers of plates that are separated and sealed. Typical flow is cross current and since the majority of plates are solid and non permeable, sensible only transfer is the result. The tempering of incoming fresh air is done by a heat or energy recovery core. In this case, the core is made of aluminum or plastic plates. Humidity levels are adjusted through the transferring of water vapor. This is done with a rotating wheel either containing a desiccant material or permeable plates.[11]The percentage of the total energy saved will depend on the efficiency of the device (up to 90%) and the latitude of the building
Heat Pipe Exchanger A heat pipe is a passive energy recovery heat exchanger that has the appearance of a common plate-finned water coil except the tubes are not interconnected. Additionally it is divided into two sections by a sealed partition. Hot air passes through one side (evaporator) and is cooled while cooler air passes through the other side (condenser). While heat pipes are sensible heat transfer exchangers, if the air conditions are such that condensation forms on the fins there can be some latent heat transfer and improved efficiency.
Heat pipes are tubes that have a capillary wick inside running the length of the tube, are evacuated and then filled with a refrigerant as the working fluid, and are permanently sealed. The working fluid is selected to meet the desired temperature conditions and is usually a Class I refrigerant. Fins are similar to conventional coils - corrugated plate, plain plate, spiral design. Tube and fin spacing are selected for appropriate pressure drop at design face velocity. HVAC systems typically use copper heat pipes with aluminum fins; other materials are available.
Run-around Loop Systems The run-around heat recovery system is a simple piping loop, containing a circulator; the loop connects a finned-tube coil in the exhaust plenum with a finned-tube coil in the make-up air plenum or AHU. The coils are connected in a closed loop via counterflow piping through which an intermediate heat transfer fluid (typically water or a freezepreventive solution) is pumped. The warm exhaust air heats the circulating fluid; this fluid then warms the cool make-up air. The heat recovery system typically operates to preheat outdoor make-up air but also to pre-cool the make-up air when the exhaust air stream is cooler than the outdoor makeup air. This system operates for sensible heat recovery only. In comfort-to-comfort applications, energy transfer is seasonally reversible—the supply air is preheated when the outdoor air is cooler than the exhaust air and precooled when the outdoor air is warmer.
Thermo-Siphon Thermosiphon refers to a method of passive heat exchange based on natural convection which circulates liquid without the necessity of a mechanical pump. This circulation can either be open-loop, as when liquid in a holding tank is passed in one direction via a heated transfer tube mounted at the bottom of the tank to a distribution point even one mounted above the originating tank - or it can be a vertical closed-loop circuit with return to the original vessel. Its intended purpose is to simplify the pumping of liquid and/or heat transfer, by avoiding the cost and complexity of a conventional liquid pump. Solar Energy
Thermosiphons are used in some liquid-based solar heating systems to heat a liquid such as water. The water is heated passively by solar energy and relies on heat energy being transferred from the sun to a solar collector. The heat from the collector can be transferred to water in two ways: directly where water circulates through the collector, or indirectly where an anti-freeze solution carries the heat from the collector and transfers it to water in the tank via a heat exchanger. Convection allows for the movement of the heated liquid out of the solar collector to be replaced by colder liquid which is in turn heated. Due to this principle, it is necessary for the water to be stored in a tank above the collector.
Heat Recovery Ventilation
Introduction
Heat recovery ventilation, also known as HRV, Mechanical ventilation heat recovery, or MVHR, is an energy recovery ventilation system, using equipment known as a heat recovery ventilator, Heat exchanger, air exchanger or air-to-air exchanger, that employs a counter-flow heat exchanger (countercurrent heat exchange) between the inbound and outbound air flow. HRV provides fresh air and improved climate control, while also saving energy by reducing the heating (or cooling) requirements. Incoming Air The air coming into the heat exchanger should be at least 0°C. Otherwise humidity in the outgoing air may condense, freeze and block the heat exchanger. A high enough incoming air temperature can also be achieved by
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recirculating some of the exhaust air (causing loss of air quality) when required, by using a very small (1 kW) heat pump to warm the inlet air above freezing before it enters the HRV. (The 'cold' side of this heatpump is situated in the warm air outlet.)
Air to Air Heat Exchanger There are a number of heat exchangers used in Heat recovery ventilation-HRV devices, as diagrammed to the right :
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cross flow heat exchanger up to 60% efficient (passive) countercurrent heat exchanger up to 99% efficient (passive) rotary heat exchanger (requires motor to turn wheel) heat pipes thin multiple heat wires (Fine wire heat exchanger)
Earth-to-Air Heat Exchanger
This can be done by an earth warming pipe ("groundcoupled heat exchanger"), usually about 30 m to 40 m long and 20 cm in diameter, typically buried about 1.5 m below ground level In high humidity areas where internal condensation could lead to fungal / mould growth in the tube leading to contamination of the air, several measures exist to prevent this.
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Ensuring the tube drains of water. Regular cleaning Tubes with an imbedded bactericide coating such as silver ions (non-toxic for humans) Air filters F7 / EU7 (>0,4 micrometres) to traps mould (of a size between 2 & 20 micrometres). UV air purification Use a earth to "water" heat exchanger.The pipes may be either corrugated/slotted to enhance heat transfer and provide condensate drainage or smooth/solid to prevent gas/liquid transfer.
Earth-to-Water Heat Exchanger
An alternative to the earth to air heat exchanger is the earth to "water" heat exchanger. This is typically similar to a geothermal heat pump tubing embedded horizontally in the soil (or could be a vertical pipe/sonde) to a similar depth of the EAHX. It uses approximately double the length of pipe Ø 35 mm ie around 80 metres compared to an EAHX. A heat exchanger coil is placed before the air inlet of the HRV. Typically a brine liquid (heavily salted water) is used as the heat exchange fluid which is slightly more efficient and environmentally friendly than polypropylene heat transfer liquids. In temperate climates in an energy efficient building, this is more than sufficient for comfort cooling during summer without resorting to an airconditioning system. In more extreme hot climates a very small air to air micro-heat pump in reverse (an air conditioner) with the evaporator (giving heat) on the air inlet after the HRV heat exchanger and the condensor (taking heat) from the air outlet after the heat exchanger will suffice.
Radiant Heating
Introduction Radiant heating is a technology for heating indoor and outdoor areas. Radiant heating consists of radiant energy being emitted from a heat source. Radiant heating heats a building through radiant heat, rather than other conventional methods including convection heating. The heat energy is emitted from a warm element, such as a floor, wall or overhead panel, and warms people and other objects
in rooms rather than directly heating the air. The internal air temperature for radiant heated buildings may be lower than for a conventionally heated building to achieve the same level of body comfort, when adjusted so the perceived temperature is actually the same. In the case of heating outdoor areas, the surrounding air is constantly moving, making conventional patio heaters, also known as "mushroom heaters", which rely partly on convection heating, impractical. The reason being, that once you heat the outside air, it will blow away with air movement. Outdoor radiant heaters allow specific spaces within an outdoor area to be targeted, warming only the people and objects in their path. The radiant heating systems can be divided into:
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Underfloor heating systems—electric or hydronic Wall heating systems Radiant ceiling (overhead) panels Trace heating- Gutter and Roof De-icing Snowmelt system- Electric or Hydronic Overhead natural gas-fired radiant heaters
Underfloor Heating Underfloor heating and cooling is a form of central heating and cooling which achieves indoor climate control for thermal comfort using conduction, radiation and convection. Description
Modern underfloor heating systems use either electrical resistance elements ("electric systems") or fluid flowing in pipes ("hydronic systems”) to heat the floor. Either type can be installed as the primary, whole-building heating system or as localized floor heating for thermal comfort. Electrical resistance can only be used for heating so when space cooling is also required, hydronic systems are used. Electric heating elements or hydronic piping can be cast in a concrete floor slab ("poured floor system" or "wet system"). They can also be placed under the floor covering ("dry system") or attached directly to a wood sub floor ("sub floor system" or "dry system").
Hydronic Systems
Hydronic systems use water or a mix of water and anti-freeze such as propylene glycol as the heat transfer fluid in a "closed loop" that is recirculated between the floor and the boiler. Various types of pipes are available specifically for hydronic underfloor heating and cooling systems and are generally made from polyethylene including PEX, PEX-Al-PEX and PERT. Older materials such as Polybutylene (PB) and copper or steel pipe are still used in some locales or for specialized applications. Hydronic systems require skilled designers and tradespeople familiar with boilers, circulators, controls, fluid pressures and temperature. The use of modern factory assembled sub-stations, used primarily in district heating and cooling, can greatly simplify design requirements and reduce the installation and commissioning time of hydronic systems. Hydronic systems can use a single source or combination of energy sources to help manage energy costs. Hydronic system energy source options are:
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Boilers (heaters) including Combined heat and power plants heated by:
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Natural gas, coal, oil or waste oil Electricity Solar thermal wood or other biomass bio-fuels
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Heat pumps and chillers powered by:
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Electricity Natural gas
Electric systems
Electric systems are used only for heating and employ noncorrosive, flexible heating elements including cables, pre-formed cable mats, bronze mesh, and carbon films. Due to their low profile they can be installed in a thermal mass or directly under floor finishes. Electric systems can also take advantage of time-of-use electricity metering and are frequently used as carpet heaters, portable under area rug heaters, under laminate floor heaters, under tile heating, under wood floor heating, and floor warming systems, including under shower floor and seat heating. Large electric systems also require skilled designers and tradespeople but this is less so for small floor warming systems. Electric systems use
fewer components and are simpler to install and commission than hydronic systems. Some electric systems use line voltage technology while others use low voltage technology. Power consumption of an electric system is not based on voltage but rather wattage output produced by the heating element.
Indoor Air
Quality
Underfloor heating can have a positive effect on the quality of indoor air by facilitating the choice of otherwise perceived cold flooring materials such as tile, slate, terrazzo and concrete. These masonry surfaces typically have very low VOC emissions (volatile organic compounds) in comparison to other flooring options. In conjunction with moisture control, floor heating also establishes temperature conditions that are less favorable in supporting mold, bacteria, viruses and dust mites. By removing the sensible heating load from the total HVAC (Heating, Ventilating, and Air Conditioning) load, ventilation, filtration and dehumidification of incoming air can be accomplished with dedicated outdoor air systems having less volumetric turnover to mitigate distribution of airborne contaminates. There is recognition from the medical community relating to
the benefits of floor heating especially as it relates to allergens. Typical Installation Details
General considerations for placing radiant heating and cooling pipes in flooring assemblies where other HVAC and plumbing components may be present.
Technical Design The amount of heat exchanged from or to an underfloor system is based on the combined radiant and convective heat transfer coefficients.
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Radiant heat transfer is constant based on the Stefan–Boltzmann constant. Convective heat transfer changes over time depending on o the air's density and thus its buoyancy. Air buoyancy changes according to surface temperatures and o forced air movement due to fans and the motion of people and objects in the space.
Convective heat transfer with underfloor systems is much greater when the system is operating in a heating rather than cooling mode. Typically with underfloor heating the convective component is almost 50% of the total heat transfer and in underfloor cooling the convective component is less than 10%. Sample - Mechanical Schematic Representation
Illustrated is a simplified mechanical schematic of an underfloor heating and cooling system for thermal comfort quality with a separate air handling system for indoor air quality. In high performance residential homes of moderate size (e.g. under 2 2 3000 ft (278 m ) total conditioned floor area), this system using manufactured hydronic control appliances would take up about the same space as a three or four piece bathroom.
Structural Insulated Panels
Structural insulated panels, SIPs, are a composite building material. They consist of an insulating layer of rigid polymer foam sandwiched between two layers of structural board. The board can be sheet metal, plywood, cement or oriented strand board
(OSB) and the foam either expanded polystyrene foam (EPS), extruded polystyrene foam (XPS) or polyurethane foam. SIPs share the same structural properties as an Ibeam or I-column. The rigid insulation core of the SIP acts as a web, while the OSB sheathing exhibits the same properties as the flanges. SIPs combine several components of conventional building, such as studs and joists, insulation, vapor barrier and air barrier. They can be used for many different applications, such as exterior wall, roof, floor and foundation systems.
Materials SIPs are most commonly made of OSB panels sandwiched around a foam core made of expanded polystyrene (EPS), extruded polystyrene (XPS) or rigid polyurethane foam, but other materials can be
used, such as plywood, pressure-treated plywood for below-grade foundation walls, steel, aluminum, cement board such as Hardibacker, and even exotic materials like stainless steel, fiber-reinforced plastic, and magnesium oxide. Some SIPs use fiber-cement or plywood sheets for the panels, and agricultural fiber, such as wheat straw, for the core. The third component in SIPs is the spline or connector piece between SIP panels. Dimensional
lumber is commonly used but creates thermal bridging and lowers insulation values. To maintain higher insulation values through the spline manufacturers use Insulated Lumber, Composite Splines, Mechanical Locks, Overlapping OSB Panels, or other creative methods. Depending on the method selected other advantages such as full nailing surfaces or increased structural strength may become available. Slab Energy Loss Even if the foundation walls under the slab are insulated, that will not help much if the slab edge close the outside air isn’t also insulated. Slab Insulation Slab insulation uses a rigid insulation material: typically foam boards. The installation is easy: just apply the right product with the right r-value under the face of the slab.
to
As the figures show, a well done slab insulation also comprises perimeter insulation, that is, insulation of the slab edge closer to the outside air. Slab Insulation Depth and R-values
The depth and the R-value recommended when insulating a slab varies with climate zones. More exactly they vary with the Heating Degree Days (HDD) of your particular climate zone. The HDD is an index reflecting the energy needs to heat or cool a home. If your climate zone has a HDD of zero that means that you do not need to insulate your slab. That happens whenever the difference between 65ºF/18ºC and the average outside temperature is very close to zero during the whole year (outside 65ºF/18ºC - «the base temperature» - is the temperature that technicians consider the ideal to get a comfortable indoor temperature; with that outside temperature, the occupants and the home appliances will add more heat to indoor home temperatures, making them comfortable). The higher the difference between the outside temperature and the 65ºF/18ºC, the higher the HDD and the needs of insulation; the higher the number of days with a high HDD, the higher the needs of insulation. The table below shows recommended R-values and slab insulation depth by the official Energy Conservation Code Council (IECC) . Recommended R-Values and Depth for Slab Insulation Heating Feet/cm Degree Installed Days Verticall (HDD) y R-Value
0 to 2,499 2,499 to 4,500 4,500 to 6,000 6,000 to 7,200 7,200 to 8,700 8,700 to 10,000 10,000 to 12,400 12,400 to 14,000
none required 2 feet/6 cm 4 feet/12 cm 4 feet/12 cm 4 feet/12 cm 4 feet/12 cm 4 feet/12 cm 4 feet/12 cm
none required R-4 R-5 R-6 R-7 R-8 R-9 R-10
Insulation of the Outside or the Inside Foundation Wall The insulation may be applied outside or inside the foundation wall. You should also apply a good finish protection (metal flashing, is a common option) and a protective termite shield (also advisable in the insulation involving the inside foundation wall).
Insulation Slab Techniques Slab insulation can be installed using foam board rigid insulation directly against the footing and the exterior of the slab, as shown in the images above.Alternatively, when building the slab you can also build "contained”/"floating" slab with interior insulation. The material is typically the same: board rigid insulation.
Photovoltaic Array
A photovoltaic array (also called a solar array) is a linked collection of photovoltaic modules, which are in turn made of multiple interconnected solar cells. The cells convert solar energy into direct current electricity via the photovoltaic effect. The power that one module can produce is seldom enough to meet requirements of a home or a business, so the modules are linked together to form an array. Most PV arrays use an inverter to convert the DC power produced by the modules into alternating current that can plug into the existing infrastructure to power lights, motors, and other loads. The modules in a PV array are usually first connected in series to obtain the desired voltage; the individual strings are then connected in parallel to allow the system to produce more current. Solar arrays are typically measured by
the peak electrical power they produce, in watts, kilowatts, or even megawatts. A photovoltaic array is a linked system of photovoltaic (PV) modules. The solar cells in the PV modules convert sunlight into electricity by bouncing the sun's photons off of silicon solar cells which produce current through the photoelectric effect. Most PV systems utilize an "inverter" to convert DC power produced by the modules to alternating current (AC) that can be used to power appliances. The solar cells are usually connected in series on the panel to achieve the desired voltage. Each individual string thereafter is connected in parallel to produce more current. Tracking systems and sensors are also placed on many solar arrays to increase the output. In some cases the increase in viable output has been up to 100%. Large scale photovoltaic arrays producing more than 1MW of electricity use solar trackers to optimize the amount of sunlight it collects. Solar collectors are another way to optimize the sunlight reaching the PV array. Solar collectors concentrate sunlight through the use of mirrors and reflective surfaces in a cost efficient way to increase the output in PV arrays. Uninsulated slabs are a cause of heating losses and uncomfortable floors and energy-inefficiency.
Heat Pumps
Air-source heat pumps (ASHP) can be thought of as reversible air conditioners. Like an air conditioner, an ASHP can take heat from a relatively cool space (e.g. a house at 70°F) and dump it into a hot place (e.g. outside at 85°F). However, unlike an air conditioner, the condenser and evaporator of an ASHP can switch roles and absorb heat from the cool outside air and dump it into a warm house. Air-source heat pumps are inexpensive relative to other heat pump systems. However, the efficiency of air-source heat pumps decline when the outdoor temperature is very cold or very hot; therefore, they are only really applicable in temperate climates. For areas not located in temperate climates, groundsource (or geothermal) heat pumps provide an efficient alternative. The difference between the two
heat pumps is that the ground-source has one of its heat exchangers placed underground—usually in a horizontal or vertical arrangement. Ground-source takes advantage of the relatively constant, mild temperatures underground, which means their efficiencies can be much greater than that of an airsource heat pump. The in-ground heat exchanger generally needs a considerable amount of area. Designers have placed them in an open area next to the building or underneath a parking lot. In terms of initial cost, the ground-source heat pump system costs about twice as much as a standard airsource heat pump to be installed. However, the upfront costs can be more than offset by the decrease in energy costs. The reduction in energy costs is especially apparent in areas with typically hot summers and cold winters. Other types of heat pumps are water-source and airearth. If the building is located near a body of water, the pond or lake could be used as a heat source or sink. Air-earth heat pumps circulate the building’s air through underground ducts. With higher fan power requirements and inefficient heat transfer, Air-earth heat pumps are generally not practical for major construction
North Walls
In an east-west oriented building, a north facing exterior wall will receive little sunlight during the winter and this will be a major source of heat loss since heat always moves toward cold. Additionally, building shading of north side open space usually renders it unusable for outdoor use. To alleviate these situations the building should be shaped so that the roof slopes downward from the south to the north wall. This reduces the height of the north face of the building and therefore the area through which
heat is lost. This also allows sunlight to reach more area of north side outdoor spaces. Variations of reducing heat loss conditions manifest in north walls include backing the building into a sloped hillside or providing a berm, both of which reduce the exposed north area.
South to north downward sloping roof reduces heat loss from the north wall and allows sunlight to reach north side open space.
Clerestories and Skylights
Many conditions make south wall heat collection for direct gain problematic, but it can be easily mitigated by the use of clerestories or skylights. Both of these features admit sunlight at the roof structure of a building and can be used to direct sunlight to a specific interior surface. They can also be used in combination with or as a supplement to a south facing glazed wall. Additionally, they provide for natural light applications, which can reduce the need and cost of artificial lighting. Clerestories are vertical south facing windows located at roof level ,Their advantages are that they
allow diffuse lighting into a room; they provide privacy; and they can be placed almost anywhere on a roof. In a compartmentalized building layout, each room can have its own source of heat and light. They should be located at a distance from a thermal storage wall that allows direct sunlight to hit the wall throughout the winter. This distance is roughly 1.5 times the height of the wall. Ceilings in rooms containing clerestories should be light in color to reflect or diffuse sunlight into the living space. Large interior spaces may have multiple clerestories arranged to allow maximum admission of sunlight. Care must be taken that they do not shade each other, so the clerestorey roof angle (from horizontal) of each clerestorey should be roughly the same angle of the sun at its lowest winter point (noon on December 21). Skylights are simply openings in a roof, which admit sunlight -they are either horizontal (a flat roof) or pitched at the same angle as the roof slope. In most cases. horizontal skylights are used with reflectors to increase the intensity of solar radiation (remember the angle of incidence). Large skylights should be provided with shading devices to prevent heat loss at night and heat gain during the summer months
Clerestory clerestories can be used to provide sunshine onto interior walls which would normally not have a clear view of winter sunlight.
. Skylights provide an alternative for direct solar gain, shading devices must be included as an integral part of the skylight to prevent overheating the space during mild periods.
Attached Green Houses
An indirect gain heating system, using a green house structure as a heat collector, is multi-purpose, practical and efficient. It also requires the most rigorous design because of its multiple nature, which affects sizing for space heating, creating ideal conditions for greenhouse conditions, and accurately predicting performance for both. The attachment of a greenhouse to the south side of a building enables the structure to benefit from the normal, heat collecting greenhouse operation. The greenhouse collects heat due to its solar exposure. This heat can be conducted through a thermal storage wall separating house and greenhouse, or can be convected to the interior space of the building. In this way the greenhouse serves both as a heat collector, and a solarium for people and plants. Generally, in cold climates, a greenhouse design would use between 0.65 and 1.5 square feet of south facing double glass greenhouse collecting surface for each square foot of floor area in the adjacent living space. In more moderate climates this can be reduced to
0.33 and 0.9 square feet. This should provide enough heat to keep the average temperature in the adjacent space between 60°F and 70°F.
It is desirable for a solar greenhouse structure to be recessed into the south facade of the building, thereby minimizing east and west exposures, which have little effect on heat collection but can be a great source of heat loss. Furthermore, heat transfer through the common wall between the greenhouse and the living space is increased in this configuration Greenhouses for heating purposes can be added to frame buildings to provide for direct heat during winter days, but such buildings, without thermal storage mass, do not have the ability nor capacity to store heat for use at night. Some designs integrating greenhouses, adjust for nighttime heating by transfer of all greenhouse heat to main building storage mass (floors, walls, etc.) for deferred use at night. This only works in moderately cold climates, because very cold climates require the residual heat collected by the
greenhouse to keep it, and its contents, from freezing at night. The common wall between the greenhouse and the building interior can be constructed of thermal mass materials (masonry, water, etc.). The greenhouse side of common walls should be dark in color (better absorber) and should receive maximum sunlight throughout the day. Wall vents and/or operable windows can be used to allow heated air directly into the interior space during the daytime. Wall thickness should be same as that provided for in an indirect gain (Trombe) wall. If water is used, its minimum thickness should be 8 inches (or 0.67 cubic feet for each square foot of south-facing glass). Masonry walls cannot absorb and transfer heat as fast as a greenhouse can collect it. As a result, temperatures in the greenhouse will fluctuate as much as 60°F on a clear day. To dampen (level out) these fluctuations, extra storage mass (such as masonry units or containers filled with water) can be placed in the greenhouse. These act as an interior heat dampening water wall (1 cubic foot of water for each square foot of south facing glass will reduce temperature fluctuations 25°F to 29°F). If water is used as the common wall between the greenhouse and the living space, temperature fluctuations will be smaller, and if more than the 0.67 cubic feet of water for each square foot of glass is used in the wall, temperature fluctuations will be further reduced.
In cold climates, it may be advantageous to utilize a heat storage, in the form of a rock bin, under the building or living space, which would act as thermal storage of heat collected during the day. Heat transfer can occur by natural convection if the building is terraced up a slope, or by use of a fan, which would transfer heat to a rock bed located in a crawl space under the floor of the structure The rock bed should spread across 75 to 100% of the floor area of the structure in cold climates, and 50 to 75% of the floor area in moderate climates. Heat from the greenhouse should be directed over the rock bed and a means of returning cold air from the bottom of the rock bed to the greenhouse should be provided. If a terraced design is used, colder air will naturally settle due to the convective loop cycle. About 1.5 to 3 cubic feet of fist-sized rock is necessary in cold climates and .5 to 1 cubic feet in temperate climates. Rock bin storage has also been used as a part of a cooling system in warmer climes.
By extending the end walls of an attached greenhouse, loss to the outside is reduced while the heat gains to the space are incresed.
Small fans (less than 0.25 H.P.) can be used to aid in the transfer of heat from collection space to more remote parts of the structure.
Roof Ponds
Roof ponds can be used both for heating during the winter months and for cooling during the summer months. For latitudes higher that 36° north, roof ponds require greater solar gain exposure as well as greater protection from loss of gained heat.
The system is simple in concept. The roof pond approach brings the differing building aspects of a building - roof, ceiling, heating (and cooling) system, and heat distribution (does away with ducts) into one system. The roof ponds of contained water are the heating (and cooling) unit. The roof/ceilings of the building act as the structural support for the roof ponds; the "radiator" device for evenly distributed heating of the spaces below; and as a waterproof roof system providing protection from the elements.
The movable insulation above the ponds is the weather protection, heating/cooling system "manager" and additional protection from the elements. Wintertime heating is comprised of daytime opening the insulating roof layer to allow solar radiation to heat the water beds; water bed warming heats the supporting structure which is also the ceiling for spaces below; heated support structure radiates heat to the space. At night the insulated roof panels close to contain heat gathered by the ponds to continue heating the spaces below. The sun in northern latitudes is at a lower angle with solar radiation traveling through a greater mass of atmosphere, which reduces its energy content by scattering and reflection. In this situation, increased area of exposure or use of solar reflection can be used to increase roof pond effectiveness. Additionally, in colder climates, the roof pond system benefits from insulating covers to prevent nighttime losses. The most beneficial insulation system is one that is multi-purpose and movable, operating only twice a day to 1) expose the ponds for heat collection, and 2) to cover the ponds to prevent heat loss at night. This insulation system is also beneficial in the summer when the roof ponds must be insulated to prevent summer heat gain. The movable insulation structure can operate in a number of ways - rolling, hinged, etc.. In climates where snow is likely, ponds can be placed in a solar attic below the sloping roof with south facing glazing to allow solar gain, and the attic ceiling can be painted o a reflective color or sheathed with a reflective material. To increase system performance, glazing for cold
climate solar ponds can be dual pane, or the ponds can contain an upper layer inflated air cell. It is important to provide a waterproof layer (membrane, etc.) at the pond support system surface to provide protections during draining of water for maintenance, and from water bed material failure and/or weather impacts. The capability to drain the ponds in an easy and non-damaging manner is important. The water should be enclosed in ultraviolet light inhibiting (prevents degradation) plastic bags, waterproof structural metal or fiberglass tanks which form the ceiling below. The top of the water containment system must be transparent and the sides/bottom a dark color. Insulation panels should be constructed so that they can be tightly sealed when closed to prevent infiltration heat loss. In some applications insulating panels can also serve as reflectors when open in order to direct more solar to the ponds.
Heat is transferred from the roof ponds through the support deck to the interior space below. The edges of the deck should be carefully insulated to reduce heat loss. The underside of the support deck serves as an interior ceiling, and all surfaces (including galvanized metal decking) should be painted. Because the system provides a "radiant" ceiling it is important that no insulation is used between the root
pond and the interior space. The one exception to this rule is at the bathroom, which generates high humidity from showers and tubs. Here, an
uninsulated ceiling can result in condensation and drippage, so effective water barriers and insulation are critical.
