Hot air

We have lived long enough, in many different houses and in different parts of our country, such that we can claim to have experienced every possible type of house heating system. We grew up in an era when an open fireplace was commonplace in one or more rooms, this being responsible for providing heat and possibly also for heating bath water. Electricity was often used directly for heating either air or water, but less so if a supply of gas was available, although I suspect those living more remotely had fewer choices. Those with a piped gas connection, often referred to as 'town gas', would have burnt this to heat water which was then moved around the house into things called 'radiators' which warm the air around them in different rooms by a process known as 'convection'. Take away the gas supply and another fuel, oil, is deployed in a very similar way although as far as I am aware nobody yet has ever seriously considered feeding this into houses through pipes laid in the street.

But then suddenly, or so it seems, we are being encouraged to install a totally different form of heating in our homes, one that uses neither gas nor oil nor does it even use electricity for directly producing heat. So where did this come from?

It seems we have to thank a French physicist called Sadi Carnot who in 1824 laid the groundwork for an engine that could transfer heat from a cooler body to a warmer one.* Then in 1852 Lord Kelvin developed the first heat pump which used a compression and expansion cycle to transfer heat from one place to another. None of these ideas were practical, however, for use in homes and it was only in the 1950s that the first heat pump using a refrigerant was developed and much later than this before such machines became commercially available. By the 1980s the world had become more concerned about energy efficiency and we saw the first governmental incentives for homeowners and businesses aimed at installing air source heat pumps. Since then further advances in technology have made them ever more efficient and versatile, able to provide both heating and cooling inside the home as well as hot water, even on a cold day.

Given such a long history one might have thought that everyone today would understand how heat pumps work and be able to see the advantages of installing them in the home. Strangely though this is not so. Quite the reverse, in fact, if social media commentaries are anything to go by. So why is this? How did we get to the position today where there is so much criticism and adverse comment focussed on these machines and so little understanding of how warmth can be taken from a place that is less warm and used to heat something to a much higher temperature?

My purpose here is not to provide an explanation of how a heat pump works - there are plenty of resources available to anyone who needs to know this - nor try to justify why we have fitted one both in our present house and also in the one we recently moved from, replacing in both cases fully functioning oil and gas boilers. What I am puzzled about, however, is why there is so much negativity about them, even amongst those whom one might consider to be very concerned about the impacts that burning fossil fuels has on our planet. Surely something that can produce heat other than by the combustion of gas or oil would be seen by everyone as something to be welcomed, worth installing even if this involves some initial disruption to the home. But apparently not. The most common comment I have seen goes something like,'What if there is a power cut? How can you heat your home then?' But both before and after installing our air source units we had power cuts, quite long ones, and the effect was the same...no heating. No gas or oil boiler will work without an electricity supply.

Perhaps the biggest grumble is over the cost, both of installing and running, which is bizarre when government grants are available for the first and, once properly set up, there is very little difference in running either system. Which brings me to my point; 'properly set up'. Two different companies in two different houses and in both cases once the work was done we were left with a system that worked to a particular set of timings and temperatures. We were also given the impression that we would be ill advised to change anything.

Gripe warning!

Air source systems use a large, well insulated water tank, fitted inside the house, with a thermostat inside. The default setting on both our installs meant that as soon as the water temperature dropped just a degree or two below the pre-set level, day or night, then this triggered the externally fitted air source unit to run in order to bring the temperature back up again. This might only take minutes but it does use electricity and in my view this default setting is often not necessary. In both houses the thermostat was fitted midway down the tank. What this means is that when the thermostat first detects a lower temperature there is still hot water in the top half of the tank; hot water will always rise to the top. For two people living in a house, showering daily and using hot water for washing and much else, our hot water tanks were big enough so that they needed only be heated once a day, a process taking only an hour or so. So would it not make more sense to ask if there is a cheap electricity rate available at any particular time and install a system to take advantage of this? Sadly in our experience this is beyond the remit of most installers. What is more pertinent in our present house is that we have solar panels on a south facing roof which means that around midday, given the right weather, electricity is being generated, for free. So why not make use of this and set the timer so the water is only heated at this time of day? Well we do now but only because we have reset the timers as they should have been set up from the start. I have no idea how much this saves us, nor do I intend to measure this but I can see that without taking into account the different individual circumstances that relate to each particular property and tailoring the timers and other settings accordingly you would be at risk of installing a less efficient (and therefore more costly) system. 

Gripe over.

I do appreciate that for many the idea of extracting heat from the cooler air outside, especially on a chilly day, may be difficult to understand but it does not end there. There are now fully functional home heating systems deployed which extract heat, not from the air, but from a water source. This might be a lake, the sea or even waste water containing sewage. This makes perfect sense since water is denser than air and is therefore less prone to rapid temperature fluctuations.

Time and again we are asked about our air source heating system...'Do you like it? Is it cheaper to run? Does it work when it is frosty outside? Is it noisy?... as well as 'How exactly does it work? My answer to this last one is always, 'It uses magic!'

* In reality cold is merely an absence of heat and this can be moved from somewhere cooler to somewhere warmer. Go to your fridge, a cold place, and turn up the dial to make it colder inside. You are moving heat from inside the fridge, a place where it is already cooler than outside.