Feature
In this application the collectors ( plastic or copper pipes ) are distributed over the area at a reasonable depth . The third variant for water ( brine ) to water heat pumps has a vertical collector . This does not require a large area of land but does call for deep drilling , which is a considerable cost factor and needs to be reconciled with the geological situation .
There is no general rule of thumb here . For example , in some cases , rocky ground may be more suitable for drilling than clay soil . The following rule applies to all types of heat pumps : Each Kelvin of higher temperature in the heat source produces a higher temperature in the evaporator and therefore leads to higher efficiency in the heat pump .
" Heat pumps are suitable in both new-builds and renovation projects to reduce energy consumption ."
• Air to air These are the simplest heat pump types . They often look very similar to a standard air conditioning split unit with a unit located outside and another unit located inside a building space .
This type can either work as a heating only device , or a device which can provide both heating and cooling by making use of the reversing valve already mentioned . In a heating mode the refrigerant leaves the compressor as a high pressure , high temperature vapour and passes into the reversing valve . The reversing valve is then positioned to heating mode - so the refrigerant passes through and heads to the indoor unit .
Cool air is blown over the indoor unit heat exchanger to remove some of the thermal energy and provide heating to the room , as heat is removed the refrigerant condenses . Having given up some of its energy the refrigerant leaves as a high pressure , slightly cooler , liquid .
The refrigerant then comes to the expansion valve and bypass , the expansion valve is closed so the liquid refrigerant passes through the non-return valve , through the filter drier and sight glass and then passes through the expansion valve because the non-return valve on this side is preventing the flow .
As the refrigerant passes through the expansion valve the refrigerant expands in volume and turns into a part liquid , part vapour mixture . This expansion in volume reduces the temperature and pressure .
The refrigerant then heads to the outdoor heat exchanger . Here , a fan is blowing outside ambient air over the coil and adding heat to the cold refrigerant . The refrigerant boils at a very low temperature and as it boils it will carry thermal energy away .
The refrigerant picks up thermal energy from the outside air and leaves the outdoor heat exchanger as a low pressure , low temperature slightly superheated vapour and heads back to the reversing valve . The revering valve then diverts this to the compressor to repeat the cycle .
If the system is switched to cooling mode , the system then acts like a “ normal split air conditioner ”. The compressor forces the high pressure , high temperature vapour refrigerant into the reversing valve , the reversing valve diverts this to the outdoor unit . The fan of the outdoor unit blows ambient air across the heat exchanger , this air will be a cooler temperature , so it carries the thermal energy of the refrigerant away . The refrigerant condenses as it loses its thermal energy . It then leaves as a high pressure , low temperature liquid refrigerant .
It then heads to the expansion valve , but this is closed so the refrigerant passes through the non-return valve ,
www . hvacronline . co . za RACA Journal I October 2021 25