Sunday, May 23, 2010

MVHR on the horizon, and under the ground?

23 May: I am now seriously researching and considering design ideas for an Mechanically Ventilated Heat Recovery (MVHR) system, perhaps using future Sunboxes as a inlet route, and perhaps combined with Ground-Air exchange. The ground pipes for the air inlet could be done along the gravel path to the south of the house. Easy to dig and lay pipes in.  The reason for this is that in a very well insulated house, the heat loss through ventilation can be double that lost through the fabric, as in the Peveril Solar house.

I don't think a 200mm deep Sunbox on its own could provide enough if you are trying to get 0.6 ac/hour into a 285 cu.m house. There is sunshine in the winter months, and a vertical sunbox picks up a surprising amount - well, I was surprised how well mine did during March. But a 200mm deep sunbox, 1.25m x 5m high would have a volume of only 1.25 cu.m, which means that to provide 0.6 ac/hr to the house, it has to be exhausted of air more than twice a minute (136 times per hour). During the Winter, it could hardly contribute much, although during the Summer, a louvre could be opened for it to give all its heat to the Ground loop sunboxes. (All these louvres could be operated from the bedroom windows.) Any microclimate creator is worth having, but is it worth the cost of the scaffolding, polycarbonate and aluminium?
     I would be prepared to try it as a research project - one of my great interests already is the 'Double Skin Facade' and a long time ago, I had thoughts of converting this south facade to glass.

The Savita Sunbox could be redeployed to pump liquid heat into the zone around a Ground-Air exchange pipe, with circulating pipes buried below the large diameter pipes - instead of being added to the GSHP ground loop. Even at only 1.5m depth, there is considerable temperature stability - and on the South side of the house, it is getting free underground heat from the field behind. And the heat coming up from the ground could pass through a Sunbox on its way up to the duct into the house.
   I must check out the ReHau site as that may be a source of info. I went to a Rehau lecture a while back, and they seem to be the experts on Ground-Air exchange. Their site mentions the AWADUKT system, although most of it could be done with conventional drainpipes.
   Now I know a lot more than I did a year ago about valves and relays, and programmable thermostats, and 'difficult' plumbing, so many more things become thinkable... and then perhaps possible.
    The pipes would all have to run upwards in an external duct, as I don't want to drill much more in our house interior.

Should I tell Mrs NC about these ideas yet? (the cost is met from my 'Aunt' research fund, but the noise of me drilling, sawing and swearing has to be suffered by her.)

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