Heat Pumps

 I'm not sure how I became interested just lately on getting a heat pump. Admittedly our gas central heating system had been giving us trouble over the years, but that was fixed recently when we'd discovered a one-way valve opposing the pump for the radiators. Hot water has always been very hot so that wasn't a bother. I'd actually got a quote for a new gas boiler a few years back but decided I didn't really want the hassle of the work and of course making all the inaccessible radiators accessible. In terms of maintenance costs our gas boiler was insignificant. About 40 years ago my next door neighbour replaced our oil-fired boiler with a new Hideaway gas boiler. The total cost was something like £150 and zero maintenance over the years apart from once hoovering out some dust.

Anyway I decided to see if I could save money by switching over to an air-source heat pump system.

I followed various links on my computer and ended up speaking to a nice lady over the phone.

She asked all sorts of technical questions about our house and its radiators and how it was rated. I know nothing about "ratings" but she said she'd deal with that during the planning and installation. It's one of those absolutely useless things probably introduced by a quango with little else to do?

Once I'd supplied all the information she'd requested I began to get a little mystified about the savings from switching over from gas but, no worries, all would be revealed once our quotation was produced.
 

 At first I didn't figure out exactly how the government was gong to help. The quotation was about £9,750 but did that take account of the £7,500 grant?

Yes, it did.. the full cost would be about £17,250. I'm now slightly puzzled because I'd previously looked on Ebay to get a feel for the cost of an air-sourced heat pump, and a few years back, I'd seen a typical "unit" was about £300. So what's going on? In a nutshell it appears I'd be paying for a suitable system at quite a high price (£9,750) and the company would be pocketing quite a large sum (£7,500). Not quite though. I looked at the market price of the specific heat pump plus a new 250L water cylinder and found these were about £5,250 and £3,500 respectively. That's £8,750 for the pair. If I were to do a DIY job it would cost only £1,000 less than the quotation which is £9,750.That leaves £8,500 for labour and odds and ends such as a maximum of 8 new radiators. In fact the subject of radiators is a bit iffy as under the contract terms none might be supplied.

Assuming a discount the installer would end up with about £10,000 for designing and completing the installation. Buried in the quotation is a reference to a days labour costing £400 so a couple of installation guys would charge £2,400 for 3 days. That means a markup of about £7,500 which oddly is the amount of the government grant.
 

 To clarify matters... before getting a survey to back up the "fixed price quotation" I'd need to pay a 10% deposit. Of course this would be refundable if the estimated figures couldn't be met, so no worries? By now I'd looked into real costs and the practical aspects of running a system. First of all.. any figures under the sun can be achieved. I mean that if you wanted a nice cosy room you just set the thermostat and the radiators would do their job. Alas, this cannot always be achieved from the magical air-source bits and pieces. In fact a sort of immersion heater would provide some of the work. Here, you should understand that physics dictates what's going on. Basically an air-source heat pump needs to be backed up by minimising heat losses and fitting better radiators. Our gas system supplies our radiators with water at around 70C then receives it back something like 50C. Why is this? Well, heat is lost to the rooms warmed by radiators and through losses in pipework. Unfortunately the builders of our house, back in 1983, when they'd installed all our copper pipes had covered them with concrete. A sort of unintentional underfloor heating system (mainly enjoyed by our cat).
 

 Within the calculations for an air-source heat pump installation one might see a difference between outgoing water to the radiators and a return temperature of only 5C. This figure would have been developed from a nominal 10C for a typical gas boiler arrangement. I was informed that in order to meet my nice cosy living room temperature we'd need to swap all our radiators and for this £800 had been included in the quotation. Hang on though.. if we needed new radiators to handle our new maximum water temperature of 50C (quoted by the air pump lady) to give us the same cosy room wouldn't that mean more heat losses? After all radiators are designed to lose heat. Wouldn't the additional heat loss just decrease the temperature of the returned water to the heat pump? It's sort of defeating the plan.
 

 OK, now let's consider outside air temperature. For example what happens in the winter when the air doesn't have much heat to extract? Bearing in mind that it's during winter we need to be cosier so wouldn't that immersion heater would need to work harder? When the air is really warm in summer and plenty of heat can be extracted from the air we don't wish to be cosy at all. Surely this means that the system is going to work best just when we don't need it and conversely it'll work worst when we really need it? I should really rest my case there.
 

 Up to now I've sort of assumed that there's a level playing field when it comes to sources of fuel, but there isn't. Electric power is measured in watts. The more watts consumed the faster goes our meter and the more it costs. Gas just flows through pipes and turns a vane whose turns change our meter reding. Consumption is measured in kilowatt hours and the agencies responsible for gas supplies work out an equivalent to electric power and this is also billed in kilowatt hours making it really easy to compare the prices of the two fuels. I imagine that somewhere there's a laboratory that takes gas samples and works out how much is needed to raise a specific quantity of water through a certain number of degrees. Essentially its calorific value. I guess the same could be done with black puddings (a pound of black pudding equals 37.5 watt hours or whatever?)

Now, here's the killer of air-sourced heat pumps. A kilowatt hour of electricity costs four times a kilowatt hour of gas... oops. To get around this there's a "mythical" efficiency for heat pumps of something like 200 to 400 percent. Alas.. this efficiency figure is worst in cold weather (say 250) and best in hot weather (say 400). Oh dear.. that means our immersion heater will be kicking in during cold weather and will be running at only a quarter of the efficiency of our gas boiler (ie. gas is a quarter the cost of electricity).

Maybe I'm missing something really important? Of course... if a house is designed and built to minimise heat losses to the outside world it would need fewer kilowatt hours to keep it cosy. However, I also missed something else. In order to reduce the dependency on "fossil" fuels we're relying more and more on solar energy and wind power. But during winter nights you can forget about solar power unless you have tons of batteries in which to store the daylight energy. How about nuclear? Maybe this will be available in adequate amounts in another 20 years?

Maybe, years in the future you'll hear on the radio. Tomorrow's weather will be calm and cool so be prepared for evening power cuts in your area and if you need to travel anywhere leave you EV in the garage and check your bicycle tyres.

Could there be the equivalent of a hosepipe ban? "In BH23 8DU it will be illegal to charge your EV this week and your household mains current will be limited to a maximum of 10 Amps (governed by your smart meter) for tomorrow evening".

You probably don't remember the miners' strikes when large areas of the country had no mains power outside their 3-day week allocation and at our Plessey factory in Liverpool we were allotted just 13 Amps of mains power for the other 4 days (only because we were working "in defence of the realm"). Even at GCHQ everything turned off one day because someone forget to top up the diesel generators!

I've just realised something. A heat pump is essentially a fridge so if everyone switched to a heat pump it would chill the planet and save us from global warming!!
 

 Actual quotation and numbers .. see later

 Return to Reception