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It is likely that any renovation project you are considering, short of the replacement of kitchen cabinets, will require some modification of the heating system. If you are demolishing and constructing partitions, you may have to move radiators or reconfigure the ducts a bit. If you are constructing an extension to the house, you will have to calculate the heat loss and analyze your existing system to see if it can accommodate the additional load. Even if your only change is the addition of windows, it's likely that the house will be losing more heat than it was previously, requiring a similar analysis. If you are constructing an addition to the house, or are adding a significant number of square feet of window to a particular room, * you must decide if it's more efficient to increase the size of your existing central system or to install separate, room-size units to supplement it. In renovations where modifications to the exterior shell are extensive, or in cases where the existing heating system is inadequate to begin with, you may decide to replace your central system. In this environmental design section we will discuss these modification options so that you can analyze your situation and come up with a direction. We recommend, however, that you consult with a mechanical engineer or with a heating- and -cooling consultant (often provided as a free service by the company that supplies your fuel) before making any changes. Be sure to consult your state’s energy conservation code for new or renovated construction to see if it allows the extent of glazing you wish to incorporate in your redesign. HEAT LOSS and GAIN Human beings can adapt to a wide range of temperatures and humidities (given adequate clothing) but are “comfortable” only when the surrounding air is within a relatively narrow range of temperatures. In winter a building’s heating system must supply heat to raise the temperature of a room to the desired level. At this point, ideally, the heating system should go off and stay off. This is never the case, however, since heat is constantly being lost to the outside. (Sometimes, even in winter, the house can pick up heat from the sun through south-facing windows. Generally, in northern climates more heat is lost than is gained.) In order for the mechanical system to maintain a constant comfortable temperature inside, it must replace the heat (measured in Btu being lost to the outside. The amount of heat lost is dependent on (1) the difference between the interior temperature and that outside, (2) the amount of surface (walls, roofs, etc.) in contact with the outside, (3) the resistance to heat transmission of materials used in the construction of the exterior walls, and (4) the amount of infiltration of cold air due to loose fits in the window sashes and doorframes and unsealed joints. A Btu (British thermal unit) is a measure of the quantity of heat. One Btu is the amount of heat necessary to raise the temperature of one pound of water one degree F.—roughly the equivalent of the amount of heat given off by one wooden match. Heat loss is measured in Btuh’s, the amount of Btu’s per hour. In order to determine heat loss it's necessary to quantify the four variables listed above: 1. The design temperature differential is the difference between the desired indoor temperature (usually 70°F.) and the usual low temperature for the geographic area of the house. The lowest temperature ever recorded for the area isn't the one used in this calculation since this low temperature may occur only rarely. When the temperature of the air dips below the design outdoor temperature, the house temperature drops only a few degrees, which is considered tolerable since it happens infrequently. Table Ill-C gives the low temperatures of many United States cities. 2. Determining the amount of surface in contact with the outside will require the calculation of roof, wall, and glazed surface areas. These calculations must be made separately since each of these composite materials has a different rate of heat loss. For instance, a 100-square-foot section of well-insulated roof will lose heat at a much slower rate than a window of the same size. 3. The materials used in construction of the exterior walls and roof are of primary concern in economical heat design. Some materials transfer heat better than others. In general, the more dense a material, the better it's as a conductor; the less dense, the better it's as an insulator. Metals, being very dense, are excellent heat conductors and for this reason are used for pots and pans. Solid wood resists the transfer of heat much better than metal. Most valuable for its heat—transfer resistance is air that's trapped in tiny pockets in blown or woven glass or plastics. Insulating materials and composite wall sections are measured by either their R or their U values. An R value is the measure of a homogeneous material’s resistance to the flow of heat. The higher the R value, the less heat is transmitted through a material, the better that material is as an insulator. Walls and floors, how ever, are constructed of more than one material, each having its own R value plus pockets of trapped air, which has some insulation value. The U value (which is used for composite wall sections and not for any single material) measures the amount of heat that actually gets through an assembly of materials. Since the U factor measures the amount of heat that leaks through a wall, the higher the U factor, the more heat lost, or conversely, the lower the U value, the better the composite material is as an insulator. The U value is the reciprocal of the total resistance. If you have the R values of some materials and want to compare them with an assembly for which you have only the U value, you may use the formula: U=1/(R+R+R...).
The U factor is the overall coefficient of heat transfer. Thus if a wall has a U factor of .3, or 3/10 of a Btu will be transferred through one square foot of the wall to the outdoors every hour for every one degree of temperature difference between the outside and the inside. [ INSULATION: There are still a number of houses that have never been insulated. In addition, there are many houses whose insulation has been rendered ineffective by moisture trapped in the wall or other conditions. One telltale sign that the walls contain little or no insulation is the buildup of condensate on the in side walls of a heated room. If the interior walls are cold, any moisture in the room (from a kettle, perhaps, or a long-running shower) will condense and make the walls wet. One way to determine if the walls are insulated is to make a test hole in a suspicious place; another is to have the house photographed in the winter with infrared film. The photographs actually show the flow of heat from gaps in the insulation and cracks. Loose-fill insulation is primarily used on buildings that have already been constructed. The loose particles, or granules, are poured or blown into the cavity of the wall. A 4” cavity between the inner and outer walls filled with loose insulation may have four times the insulation value as a wall with an empty cavity. Be sure that the insulation material that's pumped into your walls is non-carcinogenic and is fireproof. Since the insulation must be blown into the wall to fill every void, we suggest you hire a professional who has the right equipment. If you do the work yourself, wear a mask. Rigid insulation, which may be placed in the wall or on its surface (making it an option for use in renovation), is manufactured in varying thicknesses (1/2” to 6”) and materials and can be used to insulate walls, roofing, and foundations or as a combination sheathing-insulating material. Most rigid boards are made of expanded polystyrene, fiberglass, and urethane. For any new construction, such as an addition to the house, we advise using batt insulation. Batt insulation is flexible and is sold in blankets or rolls about 15” wide. These strips are designed to fit in between the stud spaces, and come in thicknesses of 2”, 3 1/2”, 5½”, 6 1/2”, and up to 13”. Batt insulation consists of mineral, rock, slag, or glass wools. The puffed material is secured between two layers of semi-flexible material (such as paper) to form batts, which are either stapled or taped to the studs. Some batts come with a vapor barrier attached for condensation control. The batts are installed with the vapor barrier facing the warm side of the space, generally the interior. Reflective insulations work on the principle that the surface of a highly polished and shiny sub stance (usually aluminum foil backed with heavy paper) will reflect up to 90 % of the radiant heat. The system must have an air space of at least 3/4” in front of the reflective material for it to work. Very often the foil is double-sided, which increases its insulating value. The foil works to reflect the heat from the interior of the house back into the house, and is effective to a limited degree in areas that don't get too cold. The principle of reflective insulation works most efficiently when the reflective properties of aluminum foil and its additional property of being an excellent vapor barrier are combined in the foil that's attached to a blanket-type insulation. ] In order to understand the importance of insulation in all exterior construction, review the following example of a typical frame exterior wall consisting of studs, siding, sheathing, and gyp sum board and the same wall with 2” of batt insulation between the studs. The uninsulated wall has a U factor of .32, whereas the insulated wall has a (lower, therefore better) U factor of .10. Were the insulation 3 1/2” thick and of a certain type, the U factor would be .08, indicating that the well-insulated wall has four times the insulation value of the plain wall. Most new construction in northern parts of the United States uses 2 X 6 studs so that 5 insulation can be used instead of the 3 1/2” variety. The number and sizes of penetrations in the wall made for windows and doors are of great importance in the calculation of heat loss, for two reasons. First, glass loses heat at a far greater rate than most other construction materials, and second, there is often infiltration around the window sashes and doorframes. The quality of the window or door, the type of glass or door panel, and the direction faced are crucial to the design of the heating system (and the cooling system, which we will not discuss here). Windows and doors, no matter how well insulated, have significantly higher (therefore worse) U values than insulated walls. In fact, at least ten times more heat is lost per square foot through a single sheet of glass than through a well-insulated wall. Heat loss can be reduced by using a specially made thermal window unit, which consists of two (and sometimes three) sheets of glass separated by sealed air spaces. Furthermore, window units with a new type of metallic coating bonded to glass are available. The manufacturer of these windows claims that the coating reduces the transmission of radiant heat, allowing most of the low winter’s sun into the room but keeping most of the radiant heat from escaping to the outside. Even with these refinements, glazed surfaces lose heat faster than insulated walls. Windows, therefore, should be planned carefully. A further argument against the indiscriminate use of glass and placement of windows is the infiltration of air into the building through cracks in operable window frames. The cold air forced into the house by the wind must be heated. (Fixed windows that are well caulked and sealed don't significantly increase infiltration.) Almost all states have energy conservation codes that set guidelines and restrictions regarding wall insulating materials and glazing. Generally, the codes require that you limit the overall heat loss from a building. If you have only 2” of insulation in the walls and plan to use single- glazed windows, you will have to restrict the number and size of the windows. On the other hand, if you have well-insulated walls and plan to use low-heat-transmitting glazing, it's likely that you will be able to install larger windows. Heat gain is as important in the environmental renovation of the house. The same good U values of the composite walls and roof that serve to keep the heat inside in the winter will be effective in keeping the heat out in the summer. Windows, on the other hand, pick up heat in different ways and must be calculated differently when it comes to heat gain. As a matter of fact, properly placed windows can be an advantage in the winter by picking up much needed heat during the day by means of solar radiation to supplement the fuel- burning system (Inset II). When it comes to heating through solar energy, direct sunlight is of great value, although the amount of heat radiated through any one window during any particular time is difficult to measure. Those same windows that serve as a source of heat when the sun shines become a liability at night as heat is lost through the glazed surfaces and during the summer when unwanted heat radiates through the glass. If you are thinking of adding or relocating windows, a number of variables should be evaluated. One of them, of course, is the potential heat loss from the window. This, however, shouldn't be your only criterion. We think that any potential view should receive highest priority. We have seen quite a number of houses that face away from the lake because the builder followed (what he thought to be) a cardinal rule: that one never places windows on the north side. If you have a view, enjoy it. Put a nice big window on that wall, make sure it's the most resistant to heat transmission available on the market, and pay the slightly higher fuel bill on the assumption that the money is well spent. If you don’t have a great view in any one direction, locate most of the windows on the south side of the house. The house will be bright in most seasons. To protect the windows from excessive summer heat gain, design some exterior screening (deciduous trees or roof overhangs) or install interior shades. As a third priority, try to avoid an unprotected western orientation for the living room and dining room, since the glare from the setting sun may make that exposure untenable on late afternoons. Last, if you don’t have a vestibule to minimize heat loss when an exterior door is opened, try to locate the door out of the wind, in an alcove, or on the less windy face of the house. HEATING SYSTEMS When we refer to a heating system we identify it by (1) the fuel that it burns and (2) the medium by which the heat is circulated through the house. E.g., you may have a gas-fired/hot-water system or one that's oil/forced air. There are primarily three major fuel types (if you don’t count the sun or wood): oil natural gas, and electricity. It is hard to say definitively which is more or less expensive, since the comparative prices of these fuels keep changing over the years. In most areas oil and gas cost about the same and electricity is much more expensive. Household distributing systems can be divided into two major categories: direct and central. Direct heating consists of room-size units usually powered by electricity. Generally, central heating systems are fueled by gas, oil, or electricity. Direct Systems The unitary, or direct, heating system uses individual electrically driven units in each room. In this system a single electric wire connects to the heating unit and provides heat for that room only. For the most part, these systems produce heat generated by the energy lost in the resistance of the wires in the unit. The room units can be mounted high or low on the wall or can surround the perimeter walls as baseboards. Baseboard electric resistance systems are relatively inexpensive to install and aren't excessively expensive to operate if the room is very well insulated and therefore has little heat loss. Many houses built or renovated in the 1950’s and 1960’s have ceiling panels containing resist ant heat coils which radiate heat downward or heating coils installed in a concrete floor slab that radiates the heat upward. Floor and ceiling radiating systems are expensive to install, somewhat less fuel-efficient, and slow to respond to temperature changes. The heat pump can be purchased as a room-sized unit or as a component of a central distributing system. It should be considered only if you require both heating and cooling and if your winters aren't too severe. The electrically powered heat pump is a refrigeration compressor in which the condenser and evaporator can be interchanged to provide both heating and cooling. In the winter, the heat pump picks up heat from the outside air to heat the interior. In the summer, the process is reversed; the heat in a room is directed to the outside. The heat pump generally consumes less electricity than conventional electric resistance units. The heating process, however, is most efficient if the outside air is above freezing. At temperatures lower than 23°F, the pump works less efficiently to extract warmth from the air and an auxiliary heating system (such as electric resistance heat) is required. Most heat pumps have electric resistance coils built into the units which are thermostatically triggered when the temperature drops below a certain point. (See the newest energy-efficient heat pump models which operate at lower temperatures.) Central Systems The central systems consist of the heating (or cooling) generating plant and the distribution system. A hot-water system generally consists of a burner, either gas or oil (and with oil you will need a fuel storage tank), and a boiler. If you are using electricity, an electric hot-water boiler can be used which contains immersion heating elements. The heated water is distributed through pipes to convectors or radiators. A forced-hot-air system consists of a fossil- fuel burner (oil or gas) and a furnace, or an electric furnace. Forced-air systems are sometimes fueled by one large heat pump (with resistant heat backup) instead of a furnace (see the paragraph above on heat pumps). Blowers push the conditioned air through ducts to supply registers in the rooms. A return-air system of some sort is required. This can take the form of a simplified system of ducts more or less paralleling the sup ply ducts, or in small houses there can be a plenum that's formed between the ceiling and the attic.
[RADIATION, CONDUCTION, CONVECTION Heat travels in three ways: radiation, conduction, and Convection. Radiant heat is transmitted in waves which travel from a warmer object to a colder one. The interesting aspect of radiation is that the waves heat the objects they reach but not the air they pass through. Conduction is the flow of heat from one part of an object to another or between objects in contact with each other. A good example of conduction is the handle of a frying pan. During cooking the handle gets hot although it's not in direct contact with the burner. Convection is the transmission of heat from a warmer to a cooler surface by means of air movement. A hot object heats the air it comes in con tact with by conduction. This heated air expands and rises. As the air give off its heat, it becomes dense and sinks to be heated once more when it comes into contact with a hot object. The flow of heated air away from a hot object and cooler air toward it constitutes a convection flow. ] HOT-WATER SYSTEMS: In a hydronic (hot- water or steam) system, water is the medium that carries the heat to the individual rooms of the house. The water is heated centrally and is distributed through hot-water pipes to radiators or convectors. Either gas or oil is burned in a cast-iron or steel boiler generally of the water-tube variety. The basic system consists of a burner, the boiler, a water main (a single water pipe designed in a loop), a number of fittings to join the pipe Segments together, baseboard units, a thermostat to regulate the heat, a pump to push the water through the circuit, and an air-cushion tank (an expansion tank) to accommodate the expanded volume of heated water in the circuit without bursting pipes or fittings. A refinement of this simple loop system is one that uses two pipes; this allows you to modulate the heat in individual rooms. Many boilers are designed to heat the domestic water (used for showers, etc.) in addition to the water that's circulated to the baseboards. (Check to see if your state’s conservation code allows the use of this kind of boiler.) Boilers that provide domestic hot water have an additional set of coils passing through the body of the boiler. The heat generated by the burner heats both sets of coils. The advantage of this system is that it's very efficient and fuel-saving in the winter when the boiler is always working. It is much less efficient in the summer when the entire boiler must work just to heat domestic hot water. A further disadvantage is that the boiler must be sized at a Btuh level large enough to provide for both needs. Furthermore, at times of peak demand, the boiler may not be able to heat the water fast enough to adequately provide enough hot water for a series of showers. This can be rectified by having a hot- water storage tank near the boiler. A recommended method of providing domestic hot water is to have a separate hot-water heater/storage tank fueled by electricity, oil, or gas. If you have hot-water heating, it's likely that you have a series-loop baseboard system since it's the one most commonly used in small houses. The system consists of one pipe that carries hot water from the boiler through each of the base boards around the perimeter of the house. The hot-water pipe circles the house and returns to the boiler. Since the pipe goes through all of the baseboards in its loop about the house, the system can be adjusted or modulated only slightly in the individual rooms by means of dampers. The water is at its hottest when it leaves the boiler and is cooler at the end of its loop (having lost much of its heat to the rooms in its travels). A single thermostat controls the room temperature for all the rooms in the series. To keep the loops short, the system often is divided into two separate loops, each one controlled by its own thermostat, and is considered “zoned”. Separate loops for the different floors or wings of the house are required by most energy conservation codes. Many old houses, apartment buildings, and brownstones are serviced by steam systems. Steam is produced in a boiler and is distributed to the radiators by pipes. Most domestic systems are one-pipe systems. The pipe that delivers the steam carries the condensate back to the boiler. (The knocking often heard in the walls of old houses occurs when incoming steam in improperly sloping pipes traps the cooler condensate and causes it to hit the pipe at the tees and elbows.) FORCED-AIR SYSTEMS: In the forced-air system the air is conditioned at a central location, pushed by blowers through ducts to each room of the house, and released through outlets (registers in the walls or floor) into the space. An additional register in the room (or in the corridor outside the room) draws in air and returns it to the conditioning plant. This process is referred to as the conditioning cycle. The components of all forced-air systems include a blower, ductwork, and registers. If heating is required, the furnace is tapped. If cooling is called for, a heat exchanger (blower unit) and a condensing unit are used. Optional features can include different types of filtration systems and humidification. Large houses generally have a system of return air ducts that parallel the supply ducts. Small buildings often use the halls or the basement as return air plenums. The advantage of this kind of system over the hot-water heater is that, in addition to heating, the same ducts can be used to cool, ventilate, humidify, dehumidify, and clean air by removing dust, cooking and smoking odors, and allergenic substances. Many people choose air systems be cause of the filtration options. The filters can re move dust and pollen from the air, making life more comfortable for people with allergies. [CALCULATION OF HEAT LOSS: (Calculate separately for each room. Use Table for calculations.) 1. Determine the gross wall area that's exposed to the outside or to unheated spaces (such as the garage or attic). The exposed walls of closets adjacent to livable rooms must be taken into consideration as well. Gross wall area = length of wall x height. 2. Measure windows and doors and determine the total area of glass per room, and the total area of doors going to the outside (or unheated spaces). Measurements for windows are taken from the outside of the sash. Doors are measured by the size of the actual door. 3. Determine net wall area exposed to the out side. Net wall area = gross watt area — total window and door area (for the room). 4. Determine ceiling area if the space above is unheated. (If there are heated rooms above, this step can be omitted.) Ceiling area = length of room X width. 5. Determine floor area if exposed to unheated space (basement or crawl space below). 6. Determine room volume (= length x width x height). 7. Using (Heat-Loss [ Factors) determine U factors for walls, windows, ceilings, and floors exposed to the outside. 8. Determine design temperature difference using Table. The design temperature difference is equal to the difference between the desired indoor temperature (usually 70 and the usual low temperature for the area where the house is to be built. The lowest temperature ever recorded for the area isn't the one used in this calculation since this low temperature occurs only rarely. (When the temperature of the air dips below the design outdoor temperature, the house temperature drops only a few degrees, which is considered tolerable since it happens infrequently.) Table Ill-C records outdoor design temperatures for different parts of the United States. 9. Calculate area x U factor for each room component (walls, windows, doors, ceilings, and floors). 10. Determine infiltration factor for window type. 11. Calculate room volume x infiltration factor. 12. Determine total heat loss per room by adding the area x U factors and the volume x infiltration factor; multiply this total by the design temperature difference. 13. Add total heat loads of each room to deter mine total house heating loss. HEAT-LOSS CALCULATIONS Room | Length of Exposed Wall | Height of Room | Gross Wall Area (Sq. Ft.) | Windows | Door | Walls | Floor | Ceiling U: Heat-loss factor; Infiltration factor. TABLE: OUTDOOR DESIGN TEMPERATURES (DEGREES FAHRENHEIT) FOR SOME CITIES IN THE UNITED STATES The most common residential distributing systems include the trunk system, which is a central plenum adjoining the furnace with small feeder lines coming off it; the radial system, with all ducts radiating out of the central location and leading directly to the outlet registers; the perimeter loop, which combines the radial concept with a loop system that surrounds the perimeter of the house. The latter system is used primarily in a slab on grade (a concrete floor that rests directly on the earth). The circulating warm air through the perimeter loop warms the concrete slab. The size and layout of the ductwork are critical to the even distribution of hot air. Ducts that are too small or make too many bends will cause problems with the delivery of heat, the balancing of the system, and noise caused by vibrations. Dampers in the ducts control the amount of heat delivered to the individual rooms. If you aren't using a particular room, you may want to close the damper. One way to balance a system is to size the ducts so that the right amount of heat is delivered to each room. Another way is to use dampers that are opened to the right aperture to allow the needed amount of hot air to flow through. Generally, you fully open the dampers in ducts feeding rooms far from the furnace and partially open ducts in rooms close to the heat source or on the lower floors (remember: heat rises). In any duct layout try to avoid changes in direction. Bends in the ducts reduce the flow of air and cause vibrations. A variation on forced-air heating is the gravity warm-air system in which ducts, without fans, are used for supply air. This system does not depend on blowers to distribute the heat, but works on the principle that hot air rises. Cooler air falls to the lower floor and is “captured” by return-air registers. These very old-fashioned systems still work to some extent, although there are often cold pockets in the houses they serve. (Some very old houses have no ducts at all. The heated air is released through large registers on the bottom floor of the house and naturally flows upward.) SYSTEM MODIFICATIONS After studying how your existing system works, you will have to decide what, if anything, you are going to do with it. If you are renovating a house, there are three approaches to the modification of the heating-and-cooling system: If the renovation is a very minor one, you may decide to leave the heating system alone (unless, of course, the system is inefficient). If you are adding windows, calculate the heat loss to determine if you need auxiliary heat. Chances are that the replacement windows are better insulated than the (smaller) ones you are removing and the heat loss will be about the same. You may have to add or move a hydronic baseboard or an air diffuser. This isn't very difficult and is covered in Section 34. If you are adding a room or a wing to the house, or if you are adding significantly to the glazing, you must do a heat-loss analysis to determine how much your existing system will be taxed. If the system was overdesigned to begin with, you will only have to modify the distribution system. If the system will be overtaxed (or if it's too small for existing needs), you have to decide whether to replace the existing central boiler or furnace with a larger one or to use individual room-size units to make up for the increased heat loss. In evaluating these alternatives you must take into consideration cost, the kind of house you have, and your construction skills. It is least ex pensive and not too difficult to add or move a radiator if your pipes or ducts are easily accessible in a basement or attic. In an apartment, the ducts or pipes might be a little harder to get to, but at the very worst you can run them along the ceiling and encase them in gypsum board. If you have more heat loss than your central system can handle, it may be more efficient to use an electric resistance heater (if there is electrical capacity to spare) than to both replace the furnace (or boiler) and modify the ducts (or pipes). DESIGNING FOR UNIT HEATERS: If you are adding a single room to your house and don't want to modify the existing system, calculate the heat loss of the new room and purchase a through-the-wall unit for heating and cooling or an electric resistance baseboard that will provide enough heat to cover the loss. If you are adding windows and aren't sure if you are overloading the existing system, calculate the heat loss for the entire house and see if it matches the capacity of the existing boiler or furnace. If it doesn’t, you may be able to use unit heaters to make up for the additional heat loss. The best way to do this is to use the unit heater in the part of the house that's now the coldest or most remote (heat carried in pipes and ducts is reduced when made to travel a very long distance), but not necessarily in the area with the new windows. Here you can increase the size of the baseboards or open the dampers to allow in more hot air. Calculate the heat loss for the entire house and subtract the heat capacity of the boiler or furnace. The difference is the amount of heat that has to be provided by unit heaters. If there is a remote, cold room in the house (with a door), calculate the heat lost from that room. If it more or less matches the difference previously calculated, purchase a unit that will heat that room and remove the room’s radiator or register. MODIFYING A HOT-AIR SYSTEM: There are two considerations in the modification of the hot- air system: the size of the furnace and the distribution system. If the heating plant isn't large enough for the needs of the renovated house, you will have to purchase a new furnace or make up the difference with unit heaters (see the paragraph above). If your renovation increases the heat loss of a particular area, you will probably have to modify the distribution system. If the new space is along the path of an existing duct of a trunk system, open the duct and add a diffuser. You will probably have to rebalance the system by adjusting dampers along the trunk and by adjusting the amount of hot air that enters the trunk from the furnace. If the new room is enclosed, you will have to worry about return air. If the return- air system is unstructured (the air drifts back to the furnace through the hail), install a vent in the door or undercut the door by about an inch. If you are installing new or additional ducts in an old house, it may be difficult to bury the ducts in existing plaster walls and ceilings. It may be easiest to run the ducts through existing closets or along existing partitions (and fur them out with new gypsum board) so as not to disturb the plasterwork or parquet flooring. Try to plan the installation so that all horizontal runs are made in the cellar and the vertical runs in closets. MODIFYING A HOT-WATER SYSTEM: If you are modifying a series-loop system you can easily cut into the system at any point and add more room heat loss rating of the baseboard in Btuh per linear foot baseboard. You must consider, however, whether the boiler is generating enough hot water to heat the entire line. To make sure the boiler is large enough for the modified house, calculate the heat loss (Inset III) and match this figure to the one on the boiler. If the heat is zoned, calculate the heat loss for the zone that's being modified. You will also have to check to see if the tubing going through the baseboard will carry the zone’s load. (If the existing tubing is too small for the new load, you have to consider changing all of the baseboards and pipes in the loop, or dividing the circuit into two separate loops, or using an electric heater.) Decide where the new baseboard will be located. The baseboard works best (by stopping down drafts) when placed under a window. When you have the baseboard rating, you can calculate the length of the baseboard for each room by using the following formula: the length of baseboard per room = room heat loss/rating of the baseboard (in Btuh per linear foot) Energy-Efficient Boilers, Furnaces, and Heat Pumps You may be replacing your heating plant as part of your renovation. Aside from the conventional boilers, furnaces, and heat pumps, new technologies have been developed by the heating industry to burn fuel more effectively and thus to conserve energy. These new heating appliances are smaller and lighter than older models, lose less heat, and produce less exhaust. We recommend that any boiler or furnace you are purchasing be sized and installed by a professional heating firm since improper installation of the unit and its exhaust system can be very dangerous. We are even more emphatic when it comes to some of the new units listed below which have very delicate controls. Choose a unit that has a good safety record and have it installed by someone recommended by the supplier. Next, select the baseboard. You must have the manufacturer’s literature in order to select baseboards, since you need the actual rating for each linear foot of baseboard, which differs from one manufacturer to another. The sample in Illustration 6 can be used as an example. To select a baseboard you will have to know the water flow in gallons per minute (gpm), which is calculated by dividing the heat loss (Btuh) for the circuit by 10,000. (Use the 4 gpm rating only when the flow is known to be over 4 gpm; otherwise use 1 gpm.) The hot-water rating must also be known; 200 degrees is commonly used in domestic systems. CONDENSING FURNACES and BOILERS: Condensing furnaces (there are some condensing boilers on the market, but the majority of appliances available are gas-fired furnaces) may be 10 % more efficient than conventional units (some manufacturers claim that their models are 20 % more efficient). This technology, which produces a cool exhaust, operates on the following principles: First, a larger heat exchanger produces cooler gas. The heat that would ordinarily go up the chimney as waste is now saved. Second, gas (natural or propane) when burned produces waste gas that contains a great deal of water vapor. The condensing furnace lowers the temperature of the gas to below the dew point, which causes the vapor to precipitate into water. The heat of vaporization yields almost 1,000 Btu’s of heat for every pound of water that's condensed. A happy consequence of less and cooler exhaust gas is the elimination of the need for the standard flued masonry chimney. Many of these systems need only a 3”-diameter PVC exhaust pipe. The condensing appliances, although more fuel-efficient, are more costly than conventional furnaces. This additional expense is attributed to the fan that's required to vent the unit, the drain age line needed to remove the condensate, and the corrosive-resistant materials required in the construction of the unit. PULSE BURNERs: The first condensing units developed were the pulse burners, which burn a controlled mixture of fuel and air in small explosions. A drawback of the original pulse units on the market was the increased noise and vibration created. AUTOMATIC FLUE DAMPERS: When the furnace (or boiler) isn't working, a lot of the heat left in the unit is lost up the chimney. An automatic flue damper closes the flue when the burner goes off and opens it again when the system goes back on. SOLAR STRATEGIES FAN-DRIVEN BURNERS: Most gas burners operate using natural draft, which often provides more air than needed to support combustion. Fan-driven burners use less air for combustion and are more efficient. The burners come with either fans that blow fuel and air into the combustion chamber (forced-draft burners) or fans installed at the exhaust end (induced-draft burners). DOMESTIC HOT-WATER COILS: Many conventional systems have coils integrated into the boiler to provide for domestic hot water. These tankless systems, although desirable since they save the initial cost of a separate hot-water heater, are considered energy-wasting because they require use of the boiler every time domestic hot water is desired, even in the summer months, when general heating isn't needed. However, modifications of boiler technology have made the integration of hot-water coils both economically feasible and fuel-conserving. To day’s new boilers are packaged with a remote, well-insulated hot-water storage tank which eliminates the need for the boiler to constantly switch on and off. NEW HEAT PUMPS: Recent improvements in heat pumps have made the units about 35 % more efficient, according to manufacturers’ claims (and while these models are still new on the market, about 40 % more expensive). Conventional heat pumps have single-speed motors which cycle on or off, requiring a surge of electric power each time. The new heat pump achieves its efficiency by varying the speeds of the electric motors and compressor. In addition, these units reduce fuel consumption during the summer by converting the heat extracted from the interior of the house and using it to produce domestic hot water. (The manufacturer advises you, however, to have a backup hot-water heater for domestic hot-water requirements in the winter.) It may be wise to remove part of the southern wall of the house and install a greenhouse (or at least a very large window) to take advantage of some of the passive* solar strategies that have been developed in the last decade. Direct Gain The most straightforward of the solar strategies is the direct-gain method, which consists of using large expanses of glass on the south side of a building. The sun’s radiant heat enters through these glazed areas and provides warmth to the space within. In this method, as in all of the passive systems, solar radiation passes through the glass in short waves, the form that light energy takes. When these short light-energy waves come into contact with a surface of any kind (walls or floors), they are absorbed and radiated as long heat waves. Since these longer heat waves can't be transmitted through the glass, they are trapped within, heating the space. There is a big difference between “passive” and “active” solar systems. An active solar heating system gathers the sun’s heat in roof-mounted collectors and can produce either hot water or hot air to be circulated through the house via conventional pipes and ducts. So far, active systems haven't proven to be very cost-effective, and aren't widely used. First, active systems are costly and cumbersome, calling for a roof that faces directly south in addition to a large storage area of water tanks or rock to hold accumulated heat. Second, the cost of installation is high, aggravated by the fact that a duplicate, conventional backup system must be installed since the sun does not shine all day, every day. Passive systems are less complicated and less expensive. To reap the maximum benefits from the day time solar gain, this heat should be stored for later use. For this purpose materials that can hold large quantities of heat for as long as possible are used. Stone and similar masonry building materials can retain heat for long periods of time and are called thermal mass. Heat that's stored in thermal mass slowly radiates back into the space and —with the exception of a small amount of heat lost through the glass by conduction—is trapped within. Double glazing and high-performance glazing only slightly reduce the amount of radiant heat being transmitted into the house, but do reduce the amount of stored heat lost through conduction. The most logical location for the thermal mass is in the floor adjacent to the windows. A concrete slab, 6” thick or more, covered with brick payers, slate, or ceramic tile, is effective if the floor isn't covered with carpeting or upholstered furniture. The major drawbacks of any solar-energy system apply to this one as well. It can't be depended on as the sole heating system since there are long periods of time when the sun does not shine. In addition, large expanses of glass lose heat at a ferocious rate and should be shuttered with insulated panels or quilted drapes when it's cold and dark. Finally, in the summer the window should be shaded and the room well ventilated to prevent overheating. Sun Spaces The sun space or greenhouse (a completely glazed, south-facing room with a thick masonry floor) is a refinement on the direct-gain system. The wall between the building and the sun space (there must be a wall, otherwise the “greenhouse” is nothing more than a large window) may be of glass or any other construction. Heat, in its short waves, enters the greenhouse and is temporarily stored in the floor’s thermal mass. Windows and doors between the house and the greenhouse are left open to allow heat from the floor to flow into the house by convection air currents. When the heat in the floor is dissipated, the windows are closed. In the hot months, sun shades are lowered over the glass and ventilation panels are left open to cool the sun space and its floor. In a further refinement, the wall between the main building and the greenhouse is constructed as a thermal mass—that is, of stone, brick, concrete, or adobe. The result is a house with a double-layered façade. The thermal wall is painted black on the greenhouse side to allow absorption of the maximum amount of heat. The heat stored in the mass radiates to both sides of the wall. Air currents, circulating inside the house, pass close to the wall, are heated, and distribute warm air to the rest of the room. The system can be “shut off” by shading the glass, by ventilating the sun space, and /or by placing insulation panels on the outside face of the thermal wall. Thermo-syphoning This method is very similar to the One above but takes up less room. The southern façade of the house is covered with large areas of glass. A wall is built directly behind the glass with an air space of about 4” between the two surfaces. The wall is generally built of heavy masonry, but could also consist of water containers. The out side surface of the wall is painted a very dark color to allow maximum heat absorption. Thermo-syphoning provides heat in two ways. The first is through the thermal mass of the wall. The stored daytime heat is available for slow radiation into the house in the evening. As an added bonus, the wall thickness (generally 12”) slows down heat transmission during the daytime hours when the sun may be too hot. (It takes about six hours for the heat to travel the full depth of the wall.) The second way involves the narrow air space between the thermal wall and the glazing. During the day the sun penetrates the glass, heating the air space. Four operable vents are placed at the top and bottom of the wall. One set is inserted in the glazing and one set in the thermal wall. On cold, bright days, the vents in the glass are closed and the ones in the masonry opened. Cool air circulates by gravitational flow (or is pushed along by fans) through the bottom vent from the house into the air space. Heated air then rises through the air space and flows through the top vent into the interior space. If the room gets too warm, the vents in the wall can be closed. At night, when the sun no longer shines, all vents are kept closed. On warm nights all vents are left open to ventilate the interior space. In the summer shading can be placed over the exterior glazing. One answer to modulating the heat is a system that blows insulating Styrofoam balls into the air space. Next: Electrical Design |
