that sounds great, doesn’t it? there are a few more little things to finish inside the house, and a bit more (ok: a lot more) outside, but everything works, the most important pieces of furniture are in place: we have the beds, a working internet connection and i’ll get the coffee machine on sunday.
the last visible bits of progress were the solar hot water tubes installed on the roof. these tubes do not heat the water directly; the tubes heat up in the sunlight and then transfer the energy to a copper manifold on the top which has water passing through it. when the controller senses thermal gain it turns on a little pump that circulates water up into the roof unit.
new heat pump technology is apparently more efficient, at least according to a manufacturers that makes both. however, i suspect they calculate that comparison on data based on standard / fairly frequent use of the electric booster which admittedly isn’t a very good way to heat water.
for us the key downside of a heat pump was the fact that it must use electricity, while the solar collector does get away without the electric booster a fair bit, at least in sunnier areas like st helens. we had one of these systems before and we were able to keep the booster off for at least half the year.
we think the fact that we have split the system will help in a few ways: first of all it is welcome redundancy – if one system is off-line for whatever reason we can still enjoy a hot shower using the other. secondly we have more capacity, and will run down the hot water slower, resulting in less water having to be heated again every day. lastly, we wanted to avoid having to pump hot water around what is a very long house, and deal with the heat losses (and wasted water) on the way.
i still feel there should be a better way to control the booster: in our experience the controller turns on the electric heater as soon as the temperature drops, e.g. after a shower. but it makes little sense to re-heat the water after the evening shower if nobody will use any more during the night, and the temperature will still be perfectly adequate in the morning. maybe if i could tap into the temperature sensors and then use another controller in combination with something as fiendishly clever as a clock and a breaker to only enable the booster during the day if the temperature drops too far (say below 30 degrees) and there is no solar gain from the roof?
for now a simple switch will have to do, and we’ll leave it mostly off. and we’ll start enjoying the house!