Air To Water Heat Pumps and Air to Air Heat Pumps use exactly the same principle which as I can hear you all asking what’s that then? Well to put it into a simple phrase you can summarise this by saying “The manipulation of the properties of refrigerant gas”. Now there are loads of good places on the web where you can get in depth technical descriptions of this process so we will just give a brief description and concentrate on the practical aspects of this technology, and how it relates to domestic and commercial applications.
If you remember from your school days that apart from absolute zero which is -273*centigrade or there about’s their will always be heat in the air. Consider when you’ve sat on a stone wall and it feels cold (well there you go that’s basically the principle of heat pumps, your bum is warmer than the wall hence warmth is transferred from you to the wall). So from the above if we have a refrigerant that is colder than the surrounding air, heat will be absorbed into the refrigerant. We can use this heat absorbed into the refrigerant and transfer this heat to an indoor unit. The heat is then given up at the indoor unit to provide generally space heating or via a heat exchanger to heat water, this water can then be used in an under floor heating circuit for instance and also to provide domestic hot water.
Let’s talk about Air to Air Heat Pumps first – In this type of system you’re using the heated refrigerant going to the indoor unit and passing air over the heated coils to provide heat to a room. This type of technology has been around for a long time but the usage of this technology in Britain is a fairly recent event. Us Brits like to use what we know so hence gas central heating has been probably the most common type of heating over the last three decades. There still tends to be a lot of misconceptions with regard these systems and what they can actually do, so let’s give a few concrete facts to help you decide if this type of technology is for you.
How Energy Efficient Are These Systems? - Well very, but a bit like fuel performance figures for cars you tend to be given the best optimum conditions with the truth somewhere in the middle. You can get energy efficiency ratings of up to a COP value of 6 and on these systems. The COP (Coefficient of Performance) value is telling you how much useful heat energy you’re getting out for every £1 pound of electrical energy you’re putting in. Hence a COP value of 5 means you will get £5 pounds of heat energy out for the £1 pound of electrical energy you’ve put in, which as I’m sure you will agree sounds very impressive. So basically the bigger the COP number the more energy efficient the system is, as a good guideline any system with a COP value of 3.6 and over can be considered to be particularly energy efficient. Here’s the slight but though with these systems and also why Britain has the perfect climate for these types of systems. Remember we said the refrigerants colder than the air hence it’s absorbing heat, so basically this COP figure we keep going on about is telling you how much heat energy is being absorbed in relation to the input energy used, now where in danger here of getting a bit to technical so let’s keep it simple.
Why Are They Suited To Our Climate - Our climate is quite temperate and for most of the population it rarely goes below -10*c, 95% of the time temperatures stays within a range of (25*c) – (-3*c). Now our refrigerant temperature is at around (-27*c) so useful heat transferred into the refrigerant will occur throughout this temperature range but as we get to zero and below it takes more input energy to get the same out hence this COP figure of say 5 drops. The system will still work and give the required heat output down to outside air temperatures of (-15*c) but this COP value will decrease the colder you get. Now the reason we said these systems are well suited for the our British climate is the fact that for around 90% of the time you will get the COP values indicated by manufacturers, but when it does get cold and go below zero the energy efficiency will drop. You can see below the COP graph of our best selling Mitsubishi Ultra Efficiency systems and see how outside air temperature affects the COP energy efficiency of this particular air source heat pump.
