Heat pumps, How do they work?
It took me more than my 5 year apprenticeship to really understand them to the fullest extent. The simplest way to explain a heat pump is that it has the ability to move heat where you want heat to go. If your house is too cold a heat pump can move heat into your house from the outside. If your house is too warm the heat pump can reverse its cycle and move heat to the outside. To understand a heat pump you have to understand the process of refrigeration. A refrigerator is like a 1 way heat pump. It has the ability to absorb heat from inside the frige/freezer box and the system then expels this heat off those black pipes most people have seen on the back side of the refrigerator. Just Imagine the freezer box is your house and the coil on the back is the unit out side. This house would then be in air conditioning.[/vc_column_text][vcex_spacing size=”30px”][/vc_column][/vc_row][vc_row][vc_column width=”1/1″][vc_column_text]Before understanding this picture you have to understand what is inside the pipes. Inside these pipes you will find 100% refrigerant. This closed system was evacuated down to almost absolute zero. When a system is properly evacuated it has conditions similar to outer space. Once a system has almost no particles left we can then add refrigerant. Refrigerant can come as many different substances but they all have one thing in common. All refrigerants can change state from liquid to vapor or from vapor to liquid. When a refrigerant turns from a liquid to a vapor it absorbs heat. When a refrigerant turns from a vapor to a liquid it expels heat. We see this naturally every day with water. Water is a refrigerant. We can boil water which makes it absorb heat and we can condense water which makes it expel heat. Have you ever used a propane bottle so much it forms frost? That is another example of a refrigerant absorbing heat. The frost builds up because the propane absorbs heat while it boils from a liquid to a gas.
The boiling point of propane is -42 C. So why doesn’t propane boil when its in a bottle? The answer is pressure. If you placed liquid propane in a bottle with no lid it would boil. If you sealed that bottle the propane would boil until the pressure in the builds up enough to “push back” on the surface of the propane. This settles everything out and no more boiling takes place. The boiling point of propane is -42 C at atmospheric pressure. If propane was in a higher pressure environment like a bottle the boiling temperature goes up accordingly. Temperature and pressure is directly related with refrigerants. If the pressure goes up the boiling point of the refrigerant goes up. If the pressure drops the boiling point drops. Now we are getting into a refrigeration cycle.
Imagine the blue and red inside the pipes is all propane. Imagine the light red is propane Liquid and the dark red is propane Vapor. On the blue side the dark blue is propane liquid and the light blue is propane vapor. Now imagine #4 is a compressor boosting the pressure of the propane and #2 is a restriction like a small pinhole forcing the pressure to drop. The small arrows represent the propane flow and the large arrows represent airflow.[/vc_column_text][/vc_column][/vc_row][vc_row][vc_column width=”1/2″][vc_column_text]
Here is the basic refrigerant cycle.
1. The propane leaves the compressor at #4 as a high temperature high pressure 100% vapor
2. As the propane flows through the coil at #1 the airflow across the coil cools the propane down to a high pressure, low temperature 100% liquid and adds heat to the air
3. The propane then forces through the pinhole restriction at #2. This restriction drops the pressure in the pipes and the refrigerant flowing out of the restriction is now a low pressure liquid
4. Heat is absorbed by the propane as air flows across #3 cooling the air and boiling the refrigerant off to a low pressure low temperature 100% vapor
5. The vapor enters the compressor and the process restarts[/vc_column_text][/vc_column][vc_column width=”1/2″][vc_single_image image=”268″ border_color=”grey” img_link_large=”yes” img_link_target=”_blank” alignment=”none”][vcex_spacing size=”30px”][vc_single_image image=”267″ border_color=”grey” img_link_large=”yes” img_link_target=”_blank” alignment=”none”][/vc_column][/vc_row][vc_row][vc_column width=”1/1″][vc_column_text]This system is absorbing heat from #3 and expelling heat at #1. Propane and Water aren’t the only refrigerants. There are hundreds of refrigerants that all have different specific jobs. Water and propane are seldom used in a refrigeration system but they are the easiest examples to use when explaining the process because most people understand the basic properties of these substances.
Once you understand a basic refrigeration cycle it is now much easier to understand that a heat pump is the same thing it just has a few extra components to reverse the refrigerant flow.
The only real difference here is the heat pump has a reversing valve that allows refrigerant to flow in the direction desired and the restriction device (expansion valve) has a bypass or check valve to allow the reversed flow.[/vc_column_text][/vc_column][/vc_row]