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70 Cards in this Set
- Front
- Back
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How does a building surface influence comfort?
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"A building surface influences comfort primarily through its SURFACE TEMPERATURE; secondarily, it slowly changes AIR TEMPERATURE." (9.1 318)
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What are significant comfort determinants especially in cooling situations?
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"Especially in cooling situations, AIR MOTION and RH are significant comfort determinants; for many activities, AIR QUALITY... for both heating and cooling." (9.1 318)
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Why are mechanical devices often needed for comfort in addition to passive means?
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"desired air and surface temperatures can often be achieved by passive means (but)... the comfort determinants of air motion, RH and air quality often require mechanical devices." (9.1 318)
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What are the THREE design stages of HVAC systems?
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The three design stages of HVAC systems are:
1) PRELIMINARY DESIGN PHASE 2) DESIGN DEVELOPMENT 3) DESIGN FINALIZING (9.2 318-319) |
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What is done during HVAC PRELIMINARY DESIGN?
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"In the preliminary design phase, the most general combinations of
COMFORT NEEDS AND CLIMATE CHARACTERISTICS are considered: Activity comfort needs are listed. An activity schedule is developed. Site energy resources are analyzed. Climate design strategies are listed. Building form alternatives are considered. Combinations of passive and active systems are considered. One or several alternatives are sized by general design guidelines." (9.2 318) |
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What are the seven steps of DESIGN DEVELOPMENT?
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Major steps of DESIGN DEVELOPMENT:
"I. Establishes design conditions. II. Determines HVAC zones. III. Estimates thermal loads on each zone. IV. Selects HVAC systems. V. Identifies HVAC components and their locations. VI. Sizes the components. VII. Lays out the system." (9.2 319) |
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How are DESIGN CONDITIONS established?
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DESIGN CONDITIONS are established by:
"A. By activity, lists the range of acceptable air and surface temperatures, air motions, relative humidities, lighting levels, and background noise levels. B. Establishes the schedule of operations. " (9.2 318) |
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How are HVAC zones determined?
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HVAC zones are determined by considering:
A. Activities B. Schedule C. Orientation D. Internal heat gains." (9.2 319) |
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During DESIGN DEVELOPMENT, what are the four thermal loads estimated for each zone?
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During DESIGN DEVELOPMENT, the four thermal loads estimated for each zone are:
"A. ...worst winter conditions. B. ... worst summer conditions. C. ...average condition or conditions that represent the great majority of the building's operating hours. D. ..annual energy consumption." (9.2 319) |
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What happens during DESIGN FINALIZING?
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During DESIGN FINALIZING, "the HVAC system designer verifies the match between the loads on each component and the component's capacity to meet the load.
Final drawings... (9.2 319) |
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Define "skin-load dominated".
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"skin-load dominated":
"...the climate dictates whether heating or cooling is the major concern." (9.3 319) |
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What is the advantage of localized heating/cooling?
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"The advantage of local systems is their ability to respond quickly to individual rooms' needs." (9.3 319)
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What are the advantages of a central system?
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In a central system,
"the equipment is contained within its own space... maintenance can be carried out without disrupting activities within those rooms." (9.3 319) |
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What is the critical decision in sizing heating equipment?
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"The critical decision in sizing the heating equipment is the DESIGN TEMPERATURE; what is the lowest reasonable outdoor temperature for which a heating device can be sized if the desired interior temperature is to be maintained?" (9.3 319)
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What is the formula for design delta t?
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design delta t =
inside temperature - outside temperature" (9.3 319) |
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How is design delta t converted to the required capacity of a building's heating equipment?
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"To convert to the required capacity of a building's heating equipment, calculate:
Btu/DD ft squared/24 h x delta t x ft squared floor area = Btu/h heating capacity." (9.3 320) |
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What is another common unit used for sizing mechanical refrigeration?
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"Another common unit for sizing mechanical refrigeration is
tons of cooling capacity, 1 ton being equivalent to the useful cooling effect of a ton of ice, or 12,000 Btu/h. heat,gain, Btu/h/12,000 = tons of cooling." (9.3 320) |
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What are the general guidelines for sizing equipment?
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"...equipment size may be estimated using these guidelines:
For ordinary equipment: 500 square ft/ton High efficiency chillers: 1000 square ft/ton" (9.3 320) |
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What is a distribution tree in heating and cooling?
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"The distribution tree is the means for delivering heating and cooling:
the 'roots' are the machines that provide the heat and cold, the 'trunk' is the main duct or pipe...to the zone to be served... the 'branches' are the many smaller ducts or pipes that lead to individual spaces." (9.3 320) |
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What is BMS?
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BMS = Building Management System (9.4 321)
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For cooling, what is the advantage of mechanical equipment over passive approaches?
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"...mechanical equipment can rapidly concentrate heating or cooling on demand." (9.5 321)
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What are the two types of heat transfer processes commonly used in building mechanical equipment?
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"The two types of heat transfer process commonly used in mechanical equipment for buildings are the
COMPRESSIVE and ABSORPTION refrigeration cycles." (9.5 321) |
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What is the COMPRESSIVE REFRIGERATION cycle?
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"...the compressive refrigeration cycle is a scheme for transferring heat from one circulated water system (chilled water) to another (condenser water). This is done by the liquefaction and evaporation of a refrigerant, during which processes it gives off and takes on heat, respectively... the heat it acquires is drawn out of the circulated water known as the CHILLED WATER, which is the medium for subsequent cooling processes...it may be said that the refrigeration cycle pumps the heat out of the chilled water system into the condenser water system." (9.5 321)
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What is the ABSORPTION REFRIGERATION CYCLE?
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The ABSORPTION REFRIGERATION CYCLE uses salt to absorb water and thereby create water vapor as a heat transfer vehicle. Using supplementary heat, the salt solution is kept concentrated so it can continue to make water vapor. (9.5 323)
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When is a generator said to be DIRECT FIRED?
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"When a fuel such as natural gas is used as the heat for the generator, it is called DIRECT FIRED." (9.5 323)
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When is a generator called INDIRECT FIRED?
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"When another heat source (such as waste heat) is used, it is called INDIRECT FIRED." (9.5 323)
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How do people generally feel decrease in air temperature in relation to air speed past the body?
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"As a general rule, people will perceive a 1 degree F decrease in air temperature for every 15 fpm increase in that air's speed past the body." (9.6 323)
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What factors affect the air motion of a ceiling fan?
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"The air motion produced by ceiling frans will vary with
the fan height above the floor, the number of fans in a space, and the fan's power, speed, and blade size." (9.6 323) |
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What does a whole-house fan do?
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"...a whole-house fan removes the hottest air from the central hallway, exhausting to the ventilated attic." (9.6 323)
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What are the advantages of unit air conditioners?
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Unit air conditioners...
"offer a low-first-cost way to provide separate zones for individual apartments, motel rooms... mask street noise for the interior... if turned on only when cooling is needed... can provide a substantial savings over the larger always-on systems." (9.6 325) |
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What is the net effect of evaporative cooling?
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"...the net effect of evaporative cooling is NO TOTAL CHANGE in the heat content (enthalpy) of the treated air; its DB temperature is LOWERED but there is an INCREASE in RH. PEOPLE feel cooler, although no change in total heat has occurred." (9.6 325)
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What is the first step towards energy savings through control of sol-air temperature?
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"Roof color is the first consideration; WHITE OR NEAR-WHITE ROOFS are the first step toward energy savings through control of sol-air temperature." (9.6 326)
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What combination resists solar heat gain most efficiently?
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"The combination of high albedo and high emittance resists solar heat gain most efficiently." (9.6 326)
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What is ALBEDO?
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ALBEDO is "overall solar reflectance" (9.6 326)
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What is the NIGHT ROOF SPRAY THERMAL STORAGE SYSTEM (NRSTS)?
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The NIGHT ROOF SPRAY THERMAL STORAGE SYSTEM (NRSTS) "cools water on a roof by night, using both night sky radiation and evaporation. The water is then stored for use the next day in building cooling." (9.6 326)
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What are two other terms for EVAPORATIVE COOLERS?
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Evaporative coolers... also termed
SWAMP COOLERS DESERT COOLERS (9.6 327) |
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How does an evaporative cooler work?
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How an evaporative cooler works:
"Great quantities of hot, dry air are blown through pads kept moist by recirculated and makeup water. The "cooled" air is then delivered to the indoor space. The effect of the gently moving cool air is to cool the body and to produce further cooling by evaporation of body moisture." (9.6 325) |
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Where should heating devices be located in a space?
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"designers usually locate heat sources below windows." (9.7 332)
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What is the formula for heat loss?
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Heat loss = U x A x delta t (9;7 332)
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Where would heating only systems be installed?
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"There are substantial areas of North America in which the summers are so mild, but winters so cold, that heating systems are installed but not cooling systems." (9.7 331)
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What are the air quality risks of fireplaces and woodburning stoves?
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"Indoor as well as outdoor air pollution is a serious issue with fireplaces and wood stoves. Combustion generates
carbon monoxide, breathable particulates, nitrogen dioxide... wood smoke can cause nose and throat irritation... trigger asthmatic attacks." (9.7 332) |
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What is the formula for heat output to a room from a wood stove?
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"The formula for hourly heat output to a room from a wood stove is
Btu/h = (V)(E)(D)(7000)/T V = useful volume of stove (cubic ft) E = % efficiency, expressed as a decimal D = density of the wood fuel T = burn time (hours) for a complete load of firewood; usually assumed 8 hour min. 7000 = Btu/lb of firewood, 20% moisture content (9.7 332) |
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What is the disadvantage of an electric resistance heater?
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Electric resistance heaters "carry the disadvantage of using high-grade energy to do a low-grade task." (9.7 334)
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What are the advantages of the electric resistance heater?
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Advantages of the electric resistance heater are
"low first cost and individual thermostatic control that can easily be used to make each room a separate heating zone." (9.7 334) |
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How are electric heaters sized?
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"Electric heaters are sized by their capacity in kilowatts
(1 kW = 3413 Btu/h). The maximum watt density allowed is 250W per LF of heater. (9.7 335) |
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Where are gas-fired heaters usually found?
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Gas-fired heaters "are often found in semioutdoor locations such as loading docks and repair shops." (9.7 335)
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What is the fuel for a gas-fired heater?
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Gas-fired heaters "are fired with either natural gas or propane." (9.7 335)
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What is the advantage of a gas-fired heater?
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The advantage of a gas-fired heater "is that they heat surfaces first rather than air, so that comfort is obtained without the need for high air temperatures. (9.7 335)
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When are high-intensity readian heaters often used?
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"When high rates of air exchange are expected, high-intensity radiant heaters are often used." (9.7 335)
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What is the disadvantage of ceiling heat?
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"The primary disadvantage of ceiling heat is that hot air stratifies just below the ceiling... the wires are hidden within the ceiling surface, and unwary occupants can puncture wires while installing hooks or additional light fixtures."(9.7 336)
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What are the main components of both hot water and forced air systems?
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Hot water and forced air systems include
a fuel a heat source a "mover" (such as a pump or fan) a distribution system, a heat exchanger or terminal within the space a control system. (9.7 336) |
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How are hot water boilers rated?
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"Hot water boilers are rated according to heating capacity by several different categories." (9.7 336)
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How is HEATING CAPACITY defined?
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HEATING CAPACITY "is the rate of useful heat output with the boiler operating under steady-state conditions, often expressed in MBh (1000Btu/h)." (9.7 336)
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What are the three boiler rating systems?
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The three systems for rating hot water boilers are:
"Heating capacity... "AFUE, the annual fuel utilization efficiency... "net I = B = R rating..." (9.7 336) |
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How is AFUE defined?
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"AFUE, the annual fuel utilization efficiency, is defined as
100% minus the losses up the stack during both on and off cycles, and the loses due to infiltration of outdoor air to replace the air used for combustion and for draft control." (9.7 336) |
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How is "net I = B = R rating" defined?
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The NET I = B = R RATING "consists ony of the heating to be delivered to the spaces and excludes the heat loss of the boiler itself." (9.7 336)
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Why should a boiler be sized correctly?
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"too small a boiler results in lower indoor temperatures at design conditions;
too large a boiler costs more and is a waste of space." (9.7 336) |
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What are the four principle arrangements for hot water baseboard and radiator systems?
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The four principle systems for hot water baseboard and radiator systems are:
(a) series perimeter loop (b) one-pipe system (c) two-pipe, reverse return (d) two-pipe, direct return (9.7 339) |
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What is hydronic heating sizing based on?
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"The calculations for the sizing of a water distribution system are based upon
the required flow the friction in the piping... (for domestic waterd supply, another factor is the vertical distance the water must be raised.)" (9.7 342) |
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What is the key to pipe sizing in a hydronic heating system?
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"The key to pipe sizing is the overall required flow rate." (9.7 342)
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In a hydronic heating system, what is actually the critical choice?
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"the critical choice is
THE HOT-WATER SUPPLY TEMPERATURE..." (9.7 343) |
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In a hydronic heating system, how is water supply temperature related to convection of heat to the space?
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In a hydronic heating system, "the higher the temperature, the smaller the convector units that discharge the heat to each space. However, higher temperatures endanger occupants... (9.7 343)
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What is the safe choice for water distribution temperature in a hydronic heating system?
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"A safer choice of average water distribution temperature is 180 degrees F..." (9.7 343)
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How is zoning accomplished in a hydronic heating system?
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Zoning in a hydronic heating system is accomplished through the use of thermostats in each zone which connect to flow control valves which regulate the flow of heat to each zone. (9.7 344)
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Where should air be drawn from to support combustion in heating equipment and why?
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Oxygen is required for combustion; oxygen comprises only 1/5 of the air, A copious amount of air should be "drawn in from outdoors at a position close to the fuel burner or (preferably) led to this location by a duct... (9.7 346)
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How is AFUE calculated?
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"Annual fuel utilization efficiency (AFUE) is
the ratio of annual fuel output energy to annual input energy, which includes any nonseason pilot input loss." (9.7 348) |
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How is COEFFICIENT OF PERFORMANCE calculated for cooling?
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COEFFICIENT OF PERFORMANCE (COP) for cooling is
"the ratio of the rate of heat removal to the rate of energy input..." (9.7 348) |
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How is COEFFICIENT OF PERFORMANCE calculated for heating?
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COEFFICIENT OF PERFORMANCE for "heating (heat pump)... is
the ratio of the rate of heat delivered to the rate of energy input..." (9.7 348) |
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What are the advantages of warm air heating systems?
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The advantages of warm air heating are:
comfort (due to uniform heating conditions throughout an area) quick warming of the area air can be cleaned by filters in the system air circulation through the system during non-heating seasons fresh air can be brought in central cooling can be done through the same system humidification can be accomplished (9.7 350) |
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What determines duct sizing in a warm air heating system?
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"Duct sizes may be selected on the basis of permissible air velocity in the duct." (9.7 351)
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