The sow arrives

So this beast is the thermal store. 195cm high by 60cm diameter. The volume is rated at 350 litres, suggesting a 50cm diameter tank and 5cm of insulation. Seems about right.

R744.com

Most commercial refrigerants are given an "R" number. For example the once-popular Freon-12 is called R12, although this particular substance has been banned since about 1994 under the Montreal Protocol because it is very damaging to the ozone layer.

The Sanyo units use Carbon Dioxide, or CO2, as the refrigerant. For reasons that Google failed to reveal, it is also known as R744.

The R744.com website tells you pretty much everything you want to know about using R744 for heating and cooling.

When suppliers go wrong

The two heat pumps weigh in over 110kg each. Unfortunately the supplier sent brackets rated to 60kg. It took a minute or two to convince the heat pump supplier that they are the wrong ones, and that the heating engineer was not going to use them. Hopefully the proper ones will arrive on Saturday.

First Fix

First fix started on 27th April 2011. After identifying the locations where the new system will link with the old, Paul has run the first of the pipes, and the first three pumps for the system. At the bottom left, with a mapgas canister leaning, on it is the heat exchanger.

This is a braised plate heat exchanger supplied by uk-exchangers.com. This device is used to provide the domestic hot water. The left hand side of it will connect to the thermal store, which in the old days would have been your boiler. The cold water passes through the right hand side, and because the heat exchanger is so efficient, it reaches to within 1c of the temperature of the water coming from the thermal store.

So far there are three pumps. The two by the door will control the flow from the two Sanyo heat pump units which will sit outside the wall on the right. The third one will circulate water from the thermal store through the heat exchanger.

Out with the old

All of this is going. The oil tank, the gas tank, the cronky old lpg boiler.

Who?

South West heat pumps distribute them.

What?

After some searching and research, it looked like heat pumps would be a non starter, because the output temperature of ground source heat pumps and HFC-based air source heat pumps is too low to plug into my existing and conventional heating system. They generally deliver water at about 50c, and then use a "conventional" electric heater to boost the temperature to 65c. They can work down to temperatures of -10c, but during the winter of 2010, North Devon experienced temperatures of -13c. The last thing you want is your heat pump not to work on the coldest night of the year.

My heating engineer, Paul Furber of Furber Heating Ltd. directed me to Sanyo heat pumps based on the CO2 cycle. These deliver water at 65c with no need for a supplementary heater.

Perfect: you can store the water directly and use it for your bath or shower, and pump it round your existing heating system. Even better, they work all the way to -25c. This should be OK, because the lowest temperature ever recorded in southwest England was -16.7c at Cullompton in Devon in January 1940.

Why?

Why heat pumps? Well I am lucky enough to have a house in Croyde, North Devon, but it isn't on mains gas. As a result, I have a monstrosity of a Calor Gas tank stuck in the middle of the garden. Also, the boiler is 15 years old, and not as efficient as a modern one.

Add to that, my gas price was 55p/litre in March 2011.

Up until January 2010, an oil-fired combi boiler was going to be the logical choice to replace it. Except that in the winter of 2010/2011 there were heating oil supply problems in southwest England caused by bad weather. By April 2011 the price of fuel oil had risen to 65p/litre, and it was only going to get worse.