Wednesday, January 29, 2014

A number of questions answered

29 January 2014: I had an enquiry from a gentleman in Bourneville, SW Birmingham who is thinking of moving to a property which will provide a south facing roof (for PV) and considering a ground source heat pump. Reading this blog has inspired him to consider solar augmentation of the GSHP.

He sent me an introduction and a list of questions, 
I'm hoping to use your lessons to get our home to the same eco-state without having to repeat some of your less successful experiments. We're a retired couple  ...... so that means reducing our UK carbon footprint as far as economically possible. An electric car .... is on order.
   ........ I think I understand the principles behind what you've done, and I like them very much. I have quite good DIY skills, but less strength, energy and agility than I did, so may well try to find a supplier or project manager who is sympathetic and not likely to stage an eco-rebellion.

My replies, with his questions in Italic:
Hi, thanks for showing such interest in what I have done on the Peveril Solar house. Haha, thanks for mentioning the eco-rebellion, yes, we had a builder who said, 'Stop Now, Im not doing anymore ecostuff!' when we wanted to include the rainwater tank and the whole house MVHR. And here are a few answers:

1) is there a list of the suppliers and model numbers for the kit you've found satisfactory anywhere on the site?
I do mention them where possible, at the time, for example providing links to their website when they get mentioned. Which item are you asking about? the Heat pump is an IVT Greenline, the supplier is Ice Energy.... (lost contact with my original plumber, but these exist locally). For PV installation, we have used local installers with whom we have established a good word of mouth relationship, not the large nationals. The Sunbox is self built, but i can help you with a suitable design solution, and with sourcing of components. The Heat Reclaim unit is from Envirovent, fitted by them. Ask me more questions sometime, such as estimating borehole location and depth.

2) Have you considered a variable speed pump for the low-pressure sunbox to flow as much water through as will keep the outflow temperature at the optimum value?
I do have a variable speed, but i found it works best running at the fastest speed because there are many metres of pipe and a number of valves to push through, and a faster speed reduces system losses while it is passing through the above ground pipework.

3) Does the heat pump you've chosen have a special heat pump mode to raise the DHW tank to the temperature required to exterminate Legionnella (55C?), or does it use a conventional electric top up?
Yes it does, it can use direct electric power to make this a speedy process, although I have disabled the direct because there is enough heat in the ground for this to be done every three weeks or so.

4) A lot of the second-hand properties here have radiators and many are ill-suited for conversion to underfloor: do you feel that would cause much worse performance, as long as the radiators are large?
It is not acceptable to use conventional radiators as their sizing calculations are assumed to work at central heating temperatures of 60-70ºC. We have a house is well enough insulated that if you do not heat it at all, it still settles down to about 15-17º in winter (from internal and sky brightness gains) but my wife likes it about 21º. UF heating is ideal in a major rebuild or new house, but you do not need underfloor heating if retrofitting - you need either double size rads (consuming too much valuable wall space) or the most acceptable solution is dynamically assisted radiators, that have a low power fan assistance on a convector unit that will only take the same space as your existing ones. Therefore, the only thing you need to do is to get a socket near to each radiator position. The amount of power used by fan is negligible compared with the power saving by using the heat pump and the cost saving by being able to use the existing pipe circuit and pump. 

This is explained on the Dimplex website:
I don't use these, because we have underfloor on the ground floor, and underfloor upstairs which is never needed. Another trick we have is an electric blanket in the bed with a timer, so when my wife (who is disabled) is put to bed, she has one hour of warmth from that, which uses less electricity than heating up water for a hot water bottle.

5) Do the bottles in your under-the stairs diurnal storage system simply sit on a patch of underfloor heating, or are they more directly coupled to the system?
They are next to the distribution manifold which is in the cupboard under stairs. This is regularly at about 40ºC when the system is working in winter. One change is that large plastic milk bottles are not pressure resistant and the water dries out. I am gradually replacing them with large soft drinks bottles which can take the pressure of expansion of the liquid. 2 litre cider or coca-cola bottles hey can be found in waste bins, or can be bought as water in the supermarket. (I use rainwater)

6) Do you have any experience with controlling the timing of electrical loads in the house to reduce PV electricity export? [This doesn't make it greener, but might improve the economics. The electric car is a case in point, if recharging isn't urgent, it can be scheduled for times when a PV surplus is expected/actually occurs.]
Absolutely! Tea at nine, washing machine at 0930, dish washer later or when the sun shines, coffee at 11am. ironing at 1200, etc etc, never use the machines when it is dark. it does make it greener because they use power from your roof directly, not from the grid coal fired power station. You can use timers to top up your immersion heat with PV power at lunchtime if you have a HW tank separate from the heat pump.

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