HVAC Flashcards
What is the oil most commonly used in residential and light commercial boilers? What’s that BTU?
No. 2 fuel oil
BTU: 137,000-141,000
What is the most efficient fossil fuel?
Natural Gas
What are the grades of fuel oil used I large commercial boilers? What’s that BTU?
No. 4 & 5
BTU: 146,800-152,000
Name some advantages of electricity for heating over oil and gas … And one major disadvantage
Easy to install, low in installation cost, simple to operate, easy to control, flexible in zoning, no storage facilities exhaust flues or supply air. Con: high cost.
What a heat pump? And how does it work?
It heats in the winter or cools in the summer. Transfers heat from one place to another using principles of refrigeration. For cooling it pumps refrigerant to a condenser where it loses heat and then to an evaporator indoors where it absorbs heat. In winter this is reversed.
Name the temperature under which a heat pump is not competitive in efficiency with oil and gas.
40 degrees F
What can you add to make a heat pump more efficient?
Hook it up to a solar system which heats between temps of 47 to 65, under which the heat pump kicks in instead. At under 40 degrees both are used.
Name 5 passive energy sources
Solar, photovoltaic, geothermal, wind, tidal
What is a degree day?
Approx. average yearly temperature difference between the outside and the inside in particular locations.
Percentage efficiency of natural gas
70-80%
Percentage efficiency of propane
70-90%
Percentage efficiency of no. 2 oil
65-85%
Percentage efficiency of anthracite coal
65-75%
Percentage efficiency of electricity
95-100%
How do you calculate a degree day?
Take the difference between an indoor temperature of 65 degrees F and the average outside temp for a 24-hr period.
Degree days are used to calculate what?
Yearly fuel consumption
What is a furnace?
They burn gas or oil to hear air which is distributed thru the building. It burns fuel inside a combustion chamber around which air is circulated by a fan. Cool return air is heated. Hot exhaust gases are vented outside.
Basic. What is a boiler?
Use fuel to heat water, then steam or hot water is used to distribute heat
Describe the difference between an upflow, a downflow and a horizontal furnace.
In an upflow the return air comes through the bottom of the unit and the heated air goes into a bonnet up top to be distributed. Down flow the opposite – used where the ducts are in crawlspace or basement and furnace is on first floor. A horizontal furnace is used where headroom is limited.
What are the possible fuels for a boiler (4)?
Gas, oil, electricity, steam
What is compressive refrigeration?
Transfer of hear during the liquefaction/evaporation of a refrigerant
What bad thing in it does Freon have?
Clourofuorocarbons (CFCs)
What has replaced CFCs?
Hydrofluorocarbons (HFCs)
Three basic components of a compressive refrigeration cycle
Compressor, condenser, evaporator
In compressive refrigeration what does a compressor do?
Takes refrigerant in a gaseous form and turns it to a liquid
In compressive refrigeration what does a condenser do?
Takes the liquid refrigerant from the compressor and releases it to latent heat, usually outside the building
In compressive refrigeration what does an evaporator do?
Takes refrigerant from the condenser and allows it to expand; as it does so it vaporizes, absorbing heat from the surroundings before entering the compressor again
What is more efficient for carrying heat, water or air?
Water
What is refrigeration by absorption? What element does it use?
Producing chilled air by the loss of heat when water evaporates. A salt solution drawers water vapor from the evaporator.
What is more efficient – an absorption regeneration system or a compressive refrigeration system?
compressive refrigeration system
Describe evaporative cooling
Water is dropped over pads or tubes through which outdoor air/water is circulated. As the free water evaporates it takes heat from the outdoor air/water which is then circulated to the indoor spaces.
In what type of climate does evaporative cooling work and why?
Hot and arid because it has the best evaporation.
What is the unit used to describe the capacity of a refrigeration system? And what is it exactly?
A ton of refrigeration. It is the cooling effect by which 1 ton of 32 degrees F ice melts to 32 degrees F water in 24 hours. Equivalent to 12,000 BTU
In general how do you determine the required capacity of a refrigeration machine?
Dividing the total heat gain in BTU/hr by 12,000.
What is the simplest type of HVAC system and how does it work?
Direct expansion (DX) also known as incremental unit. A simple unit that passes non-ducted air to be cooled over an evaporator.
Where is a DX system usually placed?
Against an exterior wall (bc it usually uses exterior air directly)
Three types of mounting for DX systems
Thru-wall, roof mounted or packaged
What is an all-air system and how does it work?
It heats or cools spaced using conditioned air alone. Heat is transported to the space using ducts.
What is a single duct system and where would it be used?
Residential and small commercial. Air is heated in a central furnace and distributed through the building at a constant volume. One central thermostat controls. Return air ducts collect and return air to unit.
What is the only way to modulate a single duct system
With dampers
Variable air volume system
Air is heated/cooled centrally and distributed at constant temperature through a single duct. At every zone a thermostat controlling a damper varies the volume of air to each space. You can also modulate the percentage of fresh air in the return for ventilation purposes.
Three pros and one con of variable air volume system
Efficient, temperature regulation, humidity control. Con: limited in capacity to compensate for extreme differentials in heating cooling needs between zones
Dual duct system (high velocity)
One hot duct and one cold duct run simultaneously allowing each space to choose which percentage of what air it needs, lots of flexibility!!!
Despite it’s flexibility what are disadvantages of high velocity system?
Inherently inefficient because you don’t need hot air in summer, etc and you always have to run both. Plus it needs bigger fans to move the air, and that requires more energy and creates more
Noise.
Reheat (constant volume) system
A system that takes return and fresh air and cools/dehumidifies then distributed in constant volume at low temps… Then in zones or reheats the air, usually with water but possibly with electricity
Terminal reheat system is one on which…
Equipment is located near conditioned spaces
Zone reheat system is…
When the reheating coils are located in ductwork that serves entire zones
What is an economize cycle?
In a reheat system it allows outdoor air to be used for cooling when temperatures are low enough, using dampers to adjust the percentages of return versus fresh.
Pros and cons of the reheat system
Humidity and temp are carefully controlled and ducts sizes are small but the system uses a lot of energy because the primary system must be both cool most of the time and then also reheated.
Multizone system
Has a central mixing unit with both hot and cool air delivering both just like a dual duct except it delivers separately to zones
What’s the disadvantage of Multizone system?
More ducts
What size building is a Multizone system used for and way
Only for medium sized building or where a mixing unit can be put on each floor
What is dew point?
Temperature at which water vapor in the air becomes saturated and turns to water, i.e. Condenses
What is Dry bulb temperature ?
Temperature of air water mixture as measured with standard dry bulb thermometer
What is wet bulb temperature and what is it measured with in what kind of temperature ?
Temp measured by a psychrometer. More critical to measure w psychrometer in high humidity, this measure indicates stress when body is at limit of perspiration
U, coefficient of heat transmission
Overall heat flow thru any combo of bldg materials
BTU/hr-ft2-F
What is a BTU - stands for and means…
British thermal unit, heat req ‘d to raise one pound-meter by 1 degree F
1 BTU equals ? Kilo joules
1 BTU = 1.055 kJ
What is the name of the environmental credo organized by designers, scientists and tree huggers in 1996
“The Natural Step”
What is conductance
How many BTU pass thru a GIVEN material in one degree F difference.
BTU/hr-ft-F
Heat produced from human bodies is measured in:
Mets (metabolic units)
What is the measure of sensible heat loss/gain thru infiltration or ventilation?
BTU/hr
Earth’s Ecosystem a(rea)
Area of Earth’s crust 5 miles high and 5 miles deep
Enthalpy
Total heat within a substance including latent and sensible
What is latent heat?
Heat the causes a state of change as in requiring to turn water into steam
Average value of latent heat per pound of moisture
1061 BTU
What is resistance?
Number of hours needed for 1 BTU to pass through 1 ft.² of a given material.
Conductance is the reciprocal of what?
Resistance is the reciprocal of conductance
What is sensible heat?
Heat that causes a change in temperature but not a change of state (50 BTU for water)
What is specific heat?
Number of BTUs/joules required to raise the temperature of a specific material by 1°F
What is the first law of thermodynamics?
Energy cannot be created nor destroyed
You get a change in temperature by subtracting what from what?
By subtracting outside air temperature from desired indoor air temperature
Why put the vapor barrier on the warm side of the insulation?
Because you don’t want condensation in your interiors…
BTU per hour or W…
Q - total heat loss through building assembly
What is emissivity?
The ability of a material to absorb and radiate heat.
Describe a JOULE words and equation
A newton-meter, the force of one Newton acting through 1 m or one over 4.18 of the heat required to raise 1 g of water by 1°C
Three ways the body loses heat… Plus a little bit through ___?
Convection, radiation, evaporation, and to a lesser extent conduction.
What is convection?
The transfer of heat through the movement of a liquid or gas… Usually air!
Convection can only cool the body went outside temperature is less than what degree Fahrenheit? Which is what?
85°F which is the average temperature of the human body
How does the body’s heat loss through evaporation work?
Moisture changes to a vapor which takes heat to do or condensation takes heat - latent heat
What is radiation?
The transfer of heat energy through electromagnetic waves
What is conduction?
Direct heat transfer through direct contact
What is the second law of thermodynamics?
Heat always flows from a higher level to a lower level.
What is the primary determinant of human comfort in a space?
Air temperature
What is the range of human comfort in degrees Fahrenheit?
69°F to 80°F
What is the range of human temperature tolerability?
60°F to 85°F
What is effective temperature ET?
A combination of air temperature, humidity, and movement
What are the relative humidity ranges for human comfort and for tolerability?
For human comfort 30°F to 65°F for tolerability 20°F to 70°F
In what season is relative humidity most important and why?
Summer because there’s a higher dependence on he lost through evaporation
Air movement makes temperatures feel ___?
Colder
What is the “viewed angle” in connection with heat gain or loss through radiation
How much of a surface is in your 360° viewable area
What is mean radiant temperature (MRT)?
The weighted average of various surface temperatures and angles of exposure, as well as sunlight present
MRT is most important in what season?
Winter!
What is operative temperature?
The average of MRT and air temperature
With what do you measure operative temperature?
A globe thermometer
What is the unit of measurement that takes account for clothing on the body? And what is the upcharge and why?
A CLO. .15 or 15% based on a men’s business suit
Ventilation is required to do these three things!
- provide oxygen and take away carbon dioxide
- remove odors
- carry away contaminants
The amount of ventilation required depends on these three things
- what activity?
- size of room
- is there smoking involved?
What is psychometry?
The study of water vapor content of air…
What are two external factors producing heat loss and two producing heat gain
Loss: air temperature and wind
Gain: air temperature and sunlight
The two basic ways of losing heat are…
- Through the building envelope
2. Infiltration
What is conductivity?
The amount of heat loss through 1 ft.² and 1 inch thick of that material
The total amount of heat loss through a given unit area of building envelope is governed by what formula?
q=UA DeltaT
U coefficient of heat transmission of all materials is calculated with what formula?
U=1/eR
When is design cooling load factor DCLF used?… And what kinds of things does it take into account?
When calculating heat gain through glazing… Type of glazing, interior shading, outdoor design temperature.
Added latent heat gain is roughly what percent of sensible heat in most occupancies?
30%… So add 30%!
What is the specific heat of air?
1.08 BTU minute feet cubed Fahrenheit hour
The design equivalent temperature difference (DETD) is used for what? And takes what complications into effect?
It’s used for calculating heat gain through all assemblies… Air temperature differences, effects of the sun, finish colors, daily temperature ranges, etc.
What is the difference between a terminal reheat system and a zone reheat system?
Both are reheat (constant volume) systems. A terminal reheat system has equipment located near the conditioned space. A zone reheat system has reheating coils located in ductwork to serve an entire zone.
In what kind of heating system is an economizer cycle used?
In a reheat (constant volume) system
What does an economizer cycle do and how does it work?
An economizer cycle uses outdoor air for cooling when temperatures are low enough. It works by adjusting dampers on the return air ducts and fresh air intakes.
What are 2 advantages of a reheat system, also called a constant volume system?
Humidity and temperature can be carefully controlled, low supply temperature means smaller duct sizes and lower fan horsepower
What is the disadvantage of a reheat system and why?
It uses more energy than some other systems because the primary air volume must be cooled most of the time, then reheated.
What is a multi zone system?
A multizone system supplies air to a central mixing unit where separate heating and cooling coils produce hot and cold airstreams. These are mixed with dampers controlled by zone thermostats, and the resulting tempered air is delivered to the zones.
What is the advantage of a multizone HVAC system?
Simultaneous cooling and heating of different zones is possible.
What is the main disadvantage of a multizone HVAC system? Because of this what size building does it normally serve?
Duct space increases rapidly as more zones are added. Medium-sized buildings or where a central mixing unit is located on each floor.
What does an all-water system have in each condition space to allow it to heat or cool?
A fan coil unit
In all-water system what does a four pipe system have that a two pipe system doesn’t?
Two separate supply pipes, one from the chiller and one from the boiler
What are two advantages of an all-water system and one disadvantage
They are an efficient way to transfer heat, they are easily controlled, but humidity control is not possible at the central unit.
In air–water systems the majority of heating and cooling is provided by what?
Fan coil units… The water does the heating and cooling, the air is used to provide humidity control, and ventilation air conditions spaces
Air-water systems are often do used where _____.
… Return air cannot be re-circulated, such as in hospitals and laboratories.
How does an air-water induction system work?
Air is supplied throughout the building under high pressure and velocity to each induction unit, where the velocity and noise are attenuated before the air passes over the coils and is heated or cooled as required.
What is the most common way to accomplish electric heating?
Lay a grid of wires in the ceiling of a room to provide radiant heating (there are radiant floors too)
What are advantages and one big disadvantage of radiant or electric systems?
Uniform, clean, inconspicuous form of heating, easily controlled with separate thermostat in each room,required for piping or ductwork. The disadvantage is that electric heat is usually expensive.
Name eight factors to use when selecting an HVAC system
Use profile of the building, building scale, control requirements, fuels available, climatic zones, integration with building structure and systems, flexibility required, economics
What is the first consideration in selecting an HVAC system?
The anticipated use and occupancy of the building
what is one reason to use a four pipe system?
A location that experiences a wide swing in temperatures during the day may need a dual duct system or four pipe system to provide flexibility and quick response as outdoor conditions change
What is one way of achieving smoke control in a high-rise building?
By providing a separate fan room on each floor. In the event of fire, the air supply on the fire floor can be switched off and all return air can be exhausted to the outside. At the same time, the dampers on the floors above and below the fire floor can be switched to full pressurization, keeping the occupant faith and preventing the spread of smoke.
What are the three steps to calculating the size of an HVAC system?
Determine the capacity of the heating and cooling equipment, determine the size of the mechanical spaces to house the equipment, and figure the space needs and layout of the distribution system of pipes and ducts.
What is the primary determinant in sizing HVAC equipment?
The total heat gains and losses the building will experience in the most extreme conditions.
What percentage of the medium to large sized building does an all air or all water system require for its mechanical room?
3% to 9% of the gross building area
What determines the length of a boiler or chiller room?
They require rooms long enough to allow for the removal of the tubes, so the room has to be slightly longer than twice the length of the equipment. Equipment rooms need to be from 12 feet to 18 feet high.
What is the most efficient shape for a duct?
A round one!
What is static head?
The pressure required to overcome the friction lost from air moving through the ducts, fittings, registers, and other components.
What percentage of overall energy consumption in the building does an HVAC system account for?
40% to 60%
What is so environmental about a dual condenser chiller?
When building heating is not needed, I heat rejection condenser sends heat to the cooling towers. When he is needed, a separate heat recovery condenser sends excess heater fan quell units or other devices. Or you can use multiple chillers with units of varying sizes instead of one large chiller, allowing the system to operate more efficiently by using the best size chiller for the load.
What is so great about gas-fired absorption-based chillers?
They do not rely on ozone-depleting refrigerants. Are commonly powered by natural gas, lower-cost. They are not as efficient, have a higher initial cost, and reject more heat two cooling towers, but they may be more efficient for large buildings.
What is so great about solar powered absorption cooling?
Absorption chillers can be even more efficient if there powered by hot-water from solar collectors. Efficiency can be increased with parabolic concentrating solar collectors to provide higher temperature water.
What is a direct contact water heater and why is it more environmental?
A direct-contact water heater heats water by passing hot gases directly through the water. Natural gas is burned to provide the flu gases the transfer sensible and latent heat to the water. The heat exchanger on the combustion chamber reclaims any heat loss from the chamber. It’s safe for human consumption!
What are the best places for direct contact water heaters?
Where there is a continuous demand for hot water, food processing, laundries, and industrial purposes.
What is a recuperative gas boiler/boiler fuel economizer?
It recovers the sensible and latent heat from the high heat of exhaust flue gases that would normally be discharged to the atmosphere, designed to cool fluegas temperatures enough to achieve condensation. Reclaimed heat used to preheat the cold water entering the boiler or to preheat combustion air.
What is displacement ventilation and why is it environmental?
And air distribution system in which supply air originates at floor level and rises to return air grills in the ceiling. Supply air is delivered close to users and does not need to be cooled as much, resulting in energy savings.
What is a water-loop heat pump?
The heating and cooling system that uses a series of heat pumps for different zones of the building, all connected to the same piping system. Some zones can be heated, some zones cool, both extracting heat from the loop, no additional energy added or removed.
What is thermal energy storage?
When you use water, ice, or rock beds to store excess heat or coolness for use at a later time.
What is the awesome advantage of ice in thermal energy storage?
Ice can store sensible heat as well as a latent heat of fusion of ice. it’s eight times as efficient as water, size wise.
What do energy recovery ventilators, also called air-to-air heat exchangers, do? Where are they most efficient?
They reclaim waste energy from the exhaust airstream and use it to condition the incoming fresh air. Very cold, hot, or humid climates, or in 24 hour buildings with continuous occupancy such as hotels and hospitals.
Name the three types of air-to-air heat exchange.
Flat plate heat recovery units, energy transfer wheels, and heat pipes
How does an energy transfer wheel or an enthalpy heat exchanger work? What chemical does it contain?
Transfers heat between two airstreams with a heat exchanger wheel, two small openings through which air passes. It uses lithium chloride.
What is a heat pipe and how does it work?
A self-contained device that transfers sensible heat energy from hot exhaust air to cool outdoor air. Hot exhaust air passes over it, vaporizing a refrigerant inside it, passing to the area of cool incoming air. As it condenses it gives off heat to the incoming air, warming it. Refrigerant passes back to the hot side by capillary action through wick material in the heat pipe.
What is a water-to-water heat exchanger sometimes called runaround coils? What is the main advantage?
It uses water or liquid to transfer heat. The incoming and exhaust airstreams do not have to be adjacent.
How does an extract-air window work?
An additional insulated glass unit is placed over the main window unit. Air is drawn up between them, warming the glass in winter, and cooling in summer.
How does a ground-coupled heat exchanger work?
Air comes into the building through pipes buried in the ground, regulating hot summer and cold winter air.
What building type is usual for a ground couple heat exchanger? And what is their main disadvantage?
Suitable only for lowrise buildings. Their disadvantage is the long run of pipes they require for efficient operation.
What is a building automation system?
A computer-based integrated system used to monitor and control building systems. It can monitor HVAC, energy management, lighting control, life safety, and security. Maybe also elevators, communications, material handling, landscape irrigation.
What is building commissioning?
The process of inspecting, testing, starting up, and adjusting building systems and then verifying and documenting that they’re operating as intended and meet the design criteria of the contract documents.
Name the seven systems that require building commissioning.
Mechanical systems, electrical systems, plumbing, sprinkler, fire management and life safety, vertical transportation, telecom and computer.
Name all the players who should take part in building commissioning.
The architect, the MEP consultants, the general contractor, the subcontractors for mechanic for MEP and so on, the owner, all others who are integral to the process.
What is an actuator?
A device in the building control system that receives commands from a controller and activates a piece of equipment.
What is annual fuel utilization efficiency?
The ratio of annual fuel output energy to annual input energy.
What is the coefficient of performance COP?
It rates the efficiency of heating or cooling equipment. Divide the rate of energy output by the rate of energy input to the equipment.
What is a controller?
A device that measures, analyzes, and initiates actions in a building control system
What is deadband?
The range of temperature within which neither heating nor cooling is called for
Ground-coupled cooling
Method of cooling a building by direct contact with the earth or circulating Air through underground tunnels
Heat seasonal performance factor
Measure of the performance of a heat pump operating in the heating cycle
Home energy rating system
Hers. Standardized system for rating the energy efficiency of her residential building, a score between 0 and 100 indicating the relative energy efficiency of a given home.
Integrated part load value
IPLV. A single number figure of merit based on EER or COP, expressing part-load deficiency for air conditioning and heat pump equipment on the basis of weighted operation at various capacities for the equipment, as determined using the applicable test method and appliance efficiency regulations.
Relative solar heat gain (RSHG)
The ratio of solar heat gain through windows, corrected for external shading, to the incident solar radiation.
Seasonal energy efficiency ratio (SEER)
The cooling output of an A/C unit or heat pump in cooling mode. The higher the SEER, the more efficient the equipment.
In an HVAC system what is a need or demand called?
A load
What is an air handler?
A fan that moves air throughout the building ductwork system.
HEPA filters HEPA filters are often used in what location?
In the downstream ductwork
What is a damper?
One or more movable blades which can control the amount of air flow within ductwork
What’s one really good reason to use an automatic damper?
Installed in a firewall to automatically close in the case of a fire
What is a terminal unit and how does it relate to a zone?
A terminal unit it’s an automated damper. There should be one corresponding to each his own.
Why install a heating coil outside of a terminal unit?
When a building doesn’t need very much heating, having a heating coil that affects only a zone is often more efficient.
What is often installed outside the terminal unit to dampen sound?
Linings and attenuators
What do GRDs stand for?
Grilles, registers, and diffusers
When air is returned to the air handling unit a certain portion is exhausted. What is a percentage of fresh air intake in an average commercial or office building?
10% to 20%
What is an example of a hybrid building system?
Ceiling fans ETA natural ventilation, reducing mechanical cooling loads
For the best diffusion of incoming air throughout the building, and air to air heat exchanger should operate under which condition?
With the exchanger located at a central forced air fan.
The exhaust capacity of a principal residential building exhaust fan should be at least what percentage of the total HVAC system air flow capacity?
50%
What compound can be used as a canary in the coal mine to warn of other build up of pollutants?
CO2
