ETECH Exam 2 HVAC

Components of an Air Source Heat Pump

compressor, condenser, evaporator, expansion valve, refrigerant (freon)

Purpose of an Air Source Heat Pump

efficiently move heat, rather than generate it, using electricity to transfer heat from the outside air to the inside for heating and in reverse to cool the inside by extracting heat

Compressor

compresses the refrigerant gas, increasing its pressure and temperature

Condenser

gas from the compressor moves to the condenser and lets off its heat in the interior (heating) or exterior (cooling)

Evaporator

absorbs heat into the system so the heat pump can distribute it

Expansion Valve

acts like a nozzle that releases the amount of refrigerant into the evaporator, dropping its pressure so it can get cold and start absorbing heat again

Refrigerant (Freon)

chemical compound that can easily change between a liquid and gas at a low temperature, doesn’t freeze, bad for the environment

Reversing Valve

changes the direction of refrigerant flow to switch between cooling and heating modes

Heat Pump Heat Exchange Process

1. outside air always has heat

2. refrigerant in the outdoor coil absorbs outside heat

3. compressor squeezes the refrigerant, heating it

4. hot refrigerant flows to the indoor coil (condenser) then releases heat into the space

5. refrigerant cools down, turns back into a liquid, and goes through the expansion valve to cool

6. repeat

Duct Section Shape - Round

best air flow, most efficient

Duct Section Shape - Rectangular

fits in tight spots, but more drag, most economic

Duct Section Shape - Oval

best of both, but harder installation

Duct Elbows - Reliability

not reliable due to slowing down airflow, making systems noisier, and reducing efficiency

Ideal Width:Depth Ratio in Ducts

1:4, anything greater results in more friction and noise

Flexible Connection

dampens vibrations then decreasing noise and structural damage, allow thermal expansion that may happen in HVAC systems, easier installation

Heat Recovery Wheel

acts like a large heat sponge that catches heat from the outgoing air and transfers it to other incoming fresh air, saving energy and allowing efficiency

Heat Recovery Wheel - Process

1. warm air (exhaust); as air leaves the building it carries heat with it

2. heat transfer: wheel rotates and absorbs this heat

3. cool/fresh air: fresh air coming in passes through the wheel and wheel transfers heat into the incoming cool air

4. energy saving: helps to preheat incoming air, reducing the amount of energy needed to warm it up, saving energy and reducing costs

Ducts Connected to the AHU

supply duct, return duct, exhaust duct, fresh air duct

Supply Duct

hot or cool air, carries conditioned air from the AHU to the rooms in the building

Return Duct

used air, brings air from rooms back to the AHU to be cooled/heated again

Exhaust Duct

air out, takes stale or vented air and moves it out of the building

Fresh Air Duct

intake, brings fresh air from outside into the AHU for circulation in the building

IN/OUT - Air Cooled Condenser/Chiller

outside, replaces cooling tower

IN/OUT - Boiller

inside

IN/OUT - Cooling Tower

outside

IN/OUT - Water-Cooled Chiller

inside

Geothermal Heat Pump

1. underground loop: uses pipes buried in the ground to absorb heat from the earth in winter or release heat into the earth in summer

2. heat transfer: heat from the earth is carried by a fluid (water/freon) through the pipes to the heat pump inside

3. heating and cooling: either extracts heat from the fluid to warm your home in winter or removes heat from your home and sends it into the earth in the summer

Geothermal Heat Pump vs. Air Source Heat Pump

geothermal heat pump uses earth’s natural heat to warm/cool so it is more efficient and consistent and better for the environment whereas air source heat pump relies on outside air

Air Handling Unit (AHU)

giant air processor that makes sure the air inside a building is clean, the right temperature, and comfortable to breathe then sends air to every room through ducts

AHU - Process

1. takes fresh air from outside and mixes it with indoor air

2. filters clean air

3. air passes through heating/cooling coil to adjust temp

4. fan pushes air into ducts to deliver to rooms

AHU - Components

filters, heating coil, cooling coil, blower/fan, (de)humidifier

Filters

clean the air by removing dust and dirt

Heating Coil

heats the air

Cooling Coil

cools the air

Blower/Fan

pushes air through ducts

Humidifier/Dehumidifier

adds/removes moisture to maintain comfortable humidity levels

Rooftop Unit (RTU)

installed on the roof, works the same as an AHU

Variable Air Volume Boxes (VAV)

smart air regulator that controls how much air goes into a room to keep it at the right temperature, adjusts the airflow automatically to make every space comfortable

VAV - Process

1. HVAC system sends air to VAV box

2. thermostat inside VAV box checks the room temp

3. if room is too warm/cold, damper adjusts to allow more/less air

4. air is then delivered to the room at the right volume to maintain temp

VAV - Components

damper, fan, controls

Damper

moveable panel inside the VAV box that controls the airflow, opens/closes based on temp

Fan

optional, help push air into room

Controls

system can be set to adjust the air volume automatically based on temp, can also be manually controlled

Why is Fresh Air delivered to Spaces

due to need for indoor air quality control

Main Duct Area Equation

A (main duct area) = Q (air flow rate in CFM)/V (velocity in ft/min)

All-Air Systems

systems that provide complete cooling and heating through air

All-Water Systems

systems that use chilled/hot water to control temp

Air-Water Systems

systems that utilize both air and water for temp control

Direct Expansion Systems

systems that contain a complete refrigeration system to provide cooled or heated air