We often get asked if we are using an air source heat pump to heat the house why can’t we reverse it and cool the house in summer? The answer is you can, all most every air source (and ground source) heat pump is reversible, you flick a switch and bingo you have heat. So why not do it? There are a number of reasons, here goes:
No 1 Renewal Heat Incentive (RHI) Air source heat pumps are eligible for government grants ONLY if they cant cool. Turn on cooling and you throw away the grant. BUT If you have a heating only heat pump and a totally separate cooling system you still get RHI, that’s why everyone uses air-conditioning to cool in houses, not air source heat pumps.
No 2 condensation. If we cool the water in the heating system, even by a few degrees below the air temperature in the room, the pipework sweats. Think of a nice cold bottle of beer, if you leave it on the side the water from the air condenses on the bottle and leaves a puddle.
So if you run cold water through radiators they too leave a puddle. Not only this, every bit of pipework in the circuit sweats too. So radiators are definitely not suitable for cooling.
How about under floor heating? If we cool the floor more than a few degrees it too will sweat, the colder it gets the wetter the floor gets. So you get cold, wet floors. Underfloor heating has another party piece, cold air doesn’t rise, it sits on the floor, so you have to lie on the floor to cool down (and get wet). The cold air won’t rise so your head is hot, and your feet are cold.
No 3 capacities. When we calculate a heat loss for a house it is typically at -2C outside and 21C inside. We assume its dark outside, no one is home, its really cold, the lights are off and the only source of heat is the heating system. In a new house the amount of heat we need to provide is about 25W for every meter of floor space. In an old house we often have to provide 100W of heating per meter of floor space. If you come home, turn on the TV, the cooker, the internet, lights and have friends and family round then each act as a contributor to heat that the heating doesn’t need to supply. In an average house the electrical use together with the human contribution you can easily generate 1kW of heat.
If the sun comes out this also acts as a heat source heating the house making life easier for the heating system. In cooling we have to combat the heat from the ambient temperature typically we would design for 30C outside with an indoor temperature of 22C. So the load is about ½ of the heating load to start.
This means the cooling load can easily be as high as 100W per metre of floor space.
So, we can assume the load in cooling and heating are the same in an old house but the cooling load is up to 4 times as high in a new house. So, to combat the cooling load you need more heat emitters, then it gets worse.
Your underfloor heating is designed to give full output at 45C flow temp in a room at 21C, a difference of 26C. In cooling the room is at 21C but the water is only 8C, a difference of only 13C.
This halves the effectiveness of any emitter in cooling over its capacity in heating.
SO to recap; in a new house you need 4 times the cooling through heat emitters that are ½ the capacity they were in heating.
So, You need 8 times as much underfloor heating in cooling, and you still get wet!
If you really want to use your heat pump to cool and heat, we offer a solution. Fan coils. You just run radiators and Under Floor Heating for the heating as normal and a totally separate cooling loop into fan coils.
Fan coils are designed to drain away the condensation through a drain and they push the cold air around making sure the room has a nice uniform temperature and no sweating.