So what did we go with for our heat source? Biomass? Heat Pumps? Geothermal? Trombe walls with rotating phase change thermal drums (a wild idea from my past!)……
Well, after lots of analysis, it turns out that the best option for us is a top efficiency gas boiler and radiators, with some good controls. Why is that? With a super insulated house the heat losses are predicted to be pretty tiny – 5kW heat load in the depths of winter. Hopefully with two boys running around the heating won’t have to be on very much. Therefore any savings will take a long time to pay off – far longer than the life of any heating plant. A combination of capital cost, annual running costs and fuel prices means that a radiator system with a gas boiler wiped the floor with other options – in our circumstances.
It’s not just a standard installation though as explained below.
The high efficiency condensing boiler is around 90% efficient. It’s also going to provide some of the hot water when the sun isn’t shining.
The house is three stories and the ground floor has a large south facing area and a large north facing area. We therefore decided to split the house into four zones, each independently time and temperature controlled.This is done using zone control valves for each zone (there are five valves in the picture as one is for the hot water cylinder).The four zones are 1) the south facing kitchen extension 2) the rest of the ground floor 3) the first floor bedrooms and study 4) the second floor bedrooms and bathroom
Each zone has a programmable thermostat. This means each zone can be set up to demand heating at different times and to different temperatures – no point heating the bedrooms during the day or downstairs at night. There is the ability to set 5 different heating times and temperature for each day. There are various functions such as ‘keep it at this temp for X hours‘, ‘turn onto frost setting for 13 days whilst I’m on holiday and revert back to normal heating the day before I return‘.
Because each is hardwired back to the master control unit, I have the opportunity to link the master control unit to my PC and use a piece of software to amend heating programs.
The big shame is that there are very few providers or mutli zone heating controls. Most of the big names just provide a controller for 1 zone. We’ve actually used a Heatmiser system that is originally designed for underfloor heating installations.
The radiators look like this for aesthetic reasons rather than efficiency. Each radiator was sized based on the expected maximum heat requirement for each room. Because of the super insulation this means that they are all pretty small. The savings in number and size of radiators was pretty similar to the cost of the wall insulation!Some of the radiators also have thermostatic radiator valves where they are not in the vicinity of a programmable stat.
The wood burner
We have plans to install a DEFRA approved stove in the sitting room. In most circumstances a wood burner won’t contribute much, but even a 5kW one could provide most of our heating – albeit in one room. It will be a bit of an experiment to see how much of the ‘shoulders’ of the heating season we can solely use it and how much the heat from it will circulate around the house. Savings are not however expected to pay for it anytime soon though.