HVAC 2 Flashcards
What is external combustion air?
Air that is brought in from outside to aid in the boilers combustion… So that it doesn’t waste the warm and humidified building air
What is the plant?
This is the place where the warm or cool water or air is created, usually in the mechanical equipment room
What is a downdraft furnace?
When the flow of forced air travels down words, reversing the flow natural for gravity
What is a lowboy?
When the furnace is reduced to 5 feet in height so that it can fit in a big closet or attic
Which way does heat flow in a condenser and which way does heat flow in an evaporator?
Evaporation takes the heat… Eva takes the heat
Condensation releases heat
What does an evaporator of chiller do? And what is it often called?
It releases the latent heat of evaporation and dissipates it into the surrounding outside air… It is often called a cooling tower
What is a blowdown and why does it exist?
It is a small valve in the base of the cooling tower which drains off dirt and minerals. Dirt and minerals are there because the loss of water in evaporation requires that water must be added, and that water usually include stirred and minerals, which when evaporated get left behind.
What is an economizer cycle?
This refers to seasonal adjustments in the source of cool air.
… Could be a pond water in the early winter in late spring… Could be cool enough air from outside
Why is it called the COP or coefficient of performance… And not simply efficiency?
This is because he pumps do not create energy, they just move it from one place to another.
COP = energy delivered/energy used
Efficiency also = energy delivered/energy used
There are only three basic categories of HVAC distribution systems. What are they?
Electrical, hydronic, and forced air
Describe the cost variation of an electrical HVAC system. What is the archetypal system?
Lowest first cost but highest lifecycle cost. Think of a radiant system… It’s advantage is that it can be turned on in selective rooms
Talk about a one pipe system, a two pipe system, the three pipe system, and a four pipe system!
The one pipe system has one line, and this means each register it’s excessively colder on the way back to the boiler.
A two pipe system can deliver to registers directly and then return from those registers, combining the return to the same boiler.
A four-pipe system allows you to heat and cool… It’s basically two separate two pipes.
A three - pipe is like a four-pipe, but it combines the returned water…. Cheaper initial piping but more expensive as the boiler and chiller deal with combined temps
What is a cold air register?
A return air register
What can an HVAC system due to eliminate infiltration in the building?
Positively pressurize the building, by running the supply fan at a greater rate than the sum of the return air fan rate and the leakage rate of the building
What is the deck temperature?
That is the temperature of the air right as it is leaving the equipment room.
In a supply duct, exterior insulation is used for _____ _____, while interior insulation is used for ______ _____. Usually.
Temperature control. Noise control.
Put all your ducts in a row.
- Single duct
- Dual duct
- Multizone
- Fan coil unit
- Variable air volume
What the term unitary system mean?
If anyone of a number of systems which act on their own to condition separated spaces… Are zones very spread out? Do you need separate heating bills? Etc
A heat pump system is just a… And a heat sink is just…
Just a group of heat pumps serving a building. And the heat sink is water circulated throughout the building.
What does the term induction refer to?
Any system where a small amount of supply air at a very high velocity is delivered to a box unit and mixed with air brought in from the room, which induces a greater airflow than just that little bit of supply air delivered.
What is another term for a squirrel cage blower?
A centrifugal fan
There’s basically three kind of filters you can use in an HVAC system. What are they?
Fibrous filters. They remove a lot of dust and lint but they must be replaced regularly.
Electrostatic filters. More expensive, producing less resistance to air movement, they can be cleaned and washed.
Activated charcoal filters. Remove odors and chemicals, only used when this is necessary. They block the flow of air. They must be replaced regularly.
What percentage of the total building does the mechanical room take up?
5% to 10% of the total floor area of the building
How many BTU would it take to melt a ton of ice over 24 hour period?
12,000 BTU hours
What is the formula for sizing a duct?
A = 144*Q_cfm/v
Where:
A is the cross sectional area
Q_cfm is the flow rate in cubic ft/min
v is the velocity measured in feet per minute
How do you determine Q_cfm?
Q_cfm = q_tot / 1.08 (T_eq - T_i)
Where:
q_tot is the total thermal load in BTU hour
T_eq is the temperature of the air supplied in the duct (55° for cooling or 140° for heating)
T_i is the desired interior temperature for the room
What is the equivalent circular diameter?
That’s the diameter that a duct would be if it were circular… And if it were it would be the most efficient shape
The definition of benchmarking
Numbers that represent the total energy consumption in BTUs per square foot for various kinds of buildings in the US… Obviously over a certain time period.
What is commissioning? And who requires that?
And organize process to ensure old building systems perform interactively according to the architectural engineering and client intent.
LEED requires it.
What does groundwater aquifer cooling and heating utilize?
The differential thermal energy in water from an underground well, cooling a building in summer, heating a building in winter.
What does geothermal energy use?
Heat contained within the earth surface, like underground geothermal springs are lava formations.
In theory what does a fuel cell do?
Combines hydrogen and oxygen to produce electricity, heat, and water… But it’s not cost-effective
What is biogas?
Gas from biomass
