HVAC Systems System Components

The science or study of heat.

The form of energy that results from the vibration of the molecules of a substance.  The faster the vibration, the more intense the heat.

Energy can be neither created nor destroyed.

• When talking about cooling a substance (AIR), we are actually referring to the removal of heat from the substance.
• Heat does not vanish.
• It is transferred from the inside air,
• to the chilled water,
• to the refrigerant,
• to the condenser,
• and finally to the outside air.

All of our lives we’ve talked about cold. As an air conditioning technician you must start to think in terms of heat (believe me, it will make things much easier when you learn about heat pumps). So, -20F is what most people would consider cold. But if you consider that absolute zero is -460F, then you can see the between cold (no heat) and -20 there is 440F.  These 440F are heat.Think of it this way. The refrigerator in your kitchen, does not add cold, it removes heat. It is designed to remove heat faster than heat can seep in through the box.

• In a typical cooling system, air is cooled when it moves through cooling coils located in the air handling unit(AHU).  
• The heat from the warmer air moves to the chilled water in the coils.
• Hines-- Chilled water is supplied to the cooling coils at approximately 42*F.
• Chilled water typically leaves the cooling coils at approximately 60*F, which indicates that the water has absorbed heat from the air.

• Let’s take two equal size pieces of iron, one is 90F and the other is 70F.
• Place them touching side by side. Immediately, the heat will flow from the hotter one until they are both equal in temperature.
• Even if you insulate between them, although it slows the process,
• the heat will flow from heat to less heat.

• When water changes state and turns to vapor,
• the liquid is giving up it’s heat in the form of vapor.

Try this, put two containers of water outside (in the summer), one with a cover and one without a cover. After several hours, measure the water temperature of both containers. The one without the cover will be 15-30F cooler because the water is evaporating (turning to vapor or changing state).  Changing the state of liquid to vapor takes a tremendous amount of heat energy, many times more than just raising the temperature of the water.Any liquid capable of boiling or changing state can be used as a refrigerant.

• 1--Conduction-via direct contact
• Conduction is the direct flow of heat through a material resulting from physical contact
• 2--Convection- via fluid
• heat transfer between a surface and adjacent fluid(gas,air or liquid) and by the flow of fluid from one place to another, induced by temperature
• 3--Radiation- via electromagnectic Radiation
• No transfer medium required
• It's the transfer of thermal energy through matter of space by electromagnectic waves.

• A high volume cooling unit. 
• The chiller acts as an evaporator.
• 

• In a refrigeration system, the mechanical device that converts
• low-pressure, low-temperature refrigerant gas into
• high-temperature, high pressure refrigerant gas.

A heat exchanger that transfers heat from the refrigerant flowing inside it to the air or water flowing over it.

• Also known as the liquid metering device or metering device. 
• Provides a pressure drop that converts the high-temperature, high-pressure liquid refrigerant from the condenser into the low-temperature, low-pressure liquid refrigerant entering the evaporator.

The transfer of heat from a warmer sustance to a cooler substance.

• Compressor – This is the heart of the central air conditioning system, and in many cases is the most expensive part to replace. Compressors typically do not fail for no reason, compressor failure is usually do to poor installation skills, moisture in system lines, over charging or under charging the unit with refrigerant, or poor air flow inside due to undersized duct work or other air flow restrictions. The compressor compresses the refrigerant from low pressure low temperature gas to high pressure high temperature liquid in order to effectively remove heat from the inside of the home.
• Condenser Coils – Another expensive part to the central air conditioning system that must be taken care of to get the most efficiency out of your unit. When outside air is blown over the condensing coils it removes the heat from the refrigerant and ejects it out the top of the unit. Washing the condensing coils with a water hose annually can ensure that they stay clean and free from obstruction such as dirt, dust and leaves.
• Fan Motor and Blade – The fan moves the air from the outside, and pulls outside ambient air across the condensing coils and ejects the heat absorbed out the top of the unit. Unlike indoor blower motors, these are usually set at one constant speed. It’s important to keep at least a 5 foot clearance above the fan motor and blade, as hanging tree limbs and leaves can actually knock the fan blade out of balance over time.
• Run Capacitor – Uses higher voltage to assist in starting and keeping the compressor and fan motor running by maintaining a correct phase of power. This is one of the most failed components and number one problem on service calls. On residential equipment there is a run capacitor for both the fan motor and the compressor, many air conditioning units these days are equipped with dual run capacitors that run the compressor and fan motor in one part.
• Contactor – This is more like a relay, and completes the 208-240 volt circuit to power the compressor and fan motor. It’s engaged by 24 volts, so when 24 volts is applied from the thermostat to the contactor, the contacts will close making the connection to allow high voltage to go to the compressor and fan motor.

Heap pump condensing units consist of the same operating parts as a cooling split system, but instead they have a reversing valve that switches the direction the refrigerant flows, and they also have a defrost control board.

• Those are the basic Hvac condensing unit parts that are required to make the outside portion of the unit run, that’s it.

• Start Capacitor – also referred to as a Hard Start, will increase the starting torque of the compressor. Many of the new Trane units come equipped with start capacitors and potential relays which remove the start capacitor once the unit is on line.
• Low Pressure / High Pressure Switches – a safety feature that will prevent the system from running if a pressure drops below a designed setting for the low side or rises above a certain pressure for the high side. Low pressure switches will engage when there is a loss of air flow or lack of refrigerant. High pressure switches will trip when the system pressure rises to high, which generates many service calls for us, especially when painters that paint building cover the units up with a paint blanket while the system is running.
• Compressor Time Delays – Prevents the compressor from short cycling or even running backwards by locking out the low voltage for a set desired time, usually between 2-5 minutes. If you have a sudden power failure, the compressor will suddenly lose power and then when power is restored will try to start again which can be detrimental to the equipment. A time delay can prevent this from happening. Although these days most of the newer digital thermostats have this feature built in to them and just need to be programmed into the thermostat.