Commercial Hvac Equitment And Troubleshooting Flashcards
(42 cards)
What are make up air units designed for ?
To filter and replace tempered air to building as the air is being exhausted
Why is a direct fired mua better than indirect muas ?
Cheaper and all the heat goes to building
Two types of mua units
Direct
Indirect
Always place burners in the outside airstream to prevent the hazardous combustion by products of indoor air contaminants. True or false
True
For proper combustion, airflow requirements across the burner must be within a specific velocity range for mua. What is it ?
2500-3200 fpm
Most direct gas fired muas have a supply air temp between _____degrees Fahrenheit and _______ degrees Fahrenheit
50 degrees Fahrenheit and 100 degrees Fahrenheit
What are profile plates in muas ?
Used to step up the velocity requirement’s
Two types of air switches in muas what are they and what do they do ?
High velocity air switches- opens when velocity of the air flowing through the unit is too high
Low velocity air switch- opens when velocity of air is lower than the set value
Isolation gas cock, main gas shut off valve, pilot gas Manual valve, pilot gas pressure regulator, pilot solenoid valve, pilot
Needle valve , pilot gas burner , main gas pressure regulator, safety shut off valve , high pressure switch and burner are all considered what on a mua system ?
Valve train
What is the valve train ?
Contains many components that add safe operation of the unit
Indirect gas. Fired systems have a sealed combustion chamber in which all products of combustion are discharged through a flue to the outside environment. True or false
True
How can u reverse a heat pump for year round climate control for homes by providing heating in winter and cooling and dehumidifying in summer ?
4 way reversing valve
What heat pump is the most commonly used ?
Air to air heat pump
How many cycles for an air to air heat pump and what are they ?
3
Heating
Cooling
Defrost
As the temp drops the ability of the heat pump to absorb heat ________
Also drops
How does a heat pump remove excess frost buildup ?
Switches into defrost mode
What is the demand frost method ?
Controls monitor airflow, refrigerant, air or coil tempature, and pressure differential across the outdoor coil to detect frost accumulation
Two types of energy revive the systems
Heat recovery ventilators (HRVS)
Energy recovery ventilators (ERV)
What does an erv do ?
Recovery’s humidity
Perfect for dry air homes using humidifier in heating seasons and and ac during cooling seasons
What does an hrv do ?
Recovers heat
Perfect for homes with excess humidity during heating
Humidifiers and hrvs work against eachother
HRVS keep excess moisture out of your home and maintain the climate at a constant level by retaing approximately ___% to ____% of heat that is normally lost through ventilation.
65% to 85%
Disadvantages of an hrv ?
Expensive to install and operate
Filter cleaning or replacement
More maintenance
10 hrv basic components
Page 28
Heat exchanger core
Circulation fans
Filters
Insulated casing
Condensate drain
Balencing damper
Installiton kit
Controls
Freeze control
Fail safe mechanism
Why do erv and hrv have drains ?
Because of temperature in heat exchanger hits dew point and needs to drain
Install a loop so smells don’t release
