Monday, April 19, 2010

Scorchio, bbrrrrrrr

The heating system has been a constant headache since day one of the project.  As a technical piece it's also held the most fascination for me after the structure itself, with a background in Physics all the theory and design appeals to my illusion that I still remember what all the mumbo-jumbo was about.  However despite being decided, its not entirely risk free the way we've gone.


The system we're installing is attempting to be cost neutral over the medium term, return over maybe 20 years at current prices, and if Carbon Tax and oil goes as expected then return shorter than that.  It should also reduce the mess and hassle of oil, namely a dripping tank and calling for for refills.


We're fitting a flat-panel solar collector and an air-source heat pump (A2W).  The solar collector is as you'd imagine - a panel set on the roof that heats a liquid (not water) that circulates through the panels into a central tank.  The A2W pump looks like an air-conditioner, sucking in air one side and drawing out latent energy, blowing cooler air out the other.  It works just like Geo-thermal but without the ground pipes which are unsuitable for our site (horizontal) or too expensive (vertical).  This too feeds into a central tank - 600L in size.


This central tank or buffer store is kept at a temperature of about 40-55 degrees by a combination of these 2 systems, with an immersion coil as a booster in the event of these failing.  From this tank, domestic hot water is acquired by drawing cold water in one end, through a large coil and emerging hot at the other end.  The water in the tank isn't directly used, the energy is transferred.  Similarly, the underfloor heating draws water from this tank and is pulled on demand into each heating zone.  A thermostat in each zone monitors the temperature and when it falls below the requires a little motor in the UFH manifold opens and lets more hot water in.


Finally, we're adding MHRV.  This is mechanical Heat-recovery Ventilation and makes a huge difference to the efficiency of the house.  Air is drawn from rooms that tend to be damper (bathrooms/kitchen), up through an air pump and out.  Air is drawn in by the same pump and a honeycomb in the middle of the pump allows the the two air flows to be close enough to transfer heat without the gases mixing.  So you get warm fresh air pumped into rooms such as bedrooms and living rooms.  The motor only uses the energy of a light bulb.


The risk we're taking?  Well - the size of our build suggests a bigger heat pump than we're installing... but I'm heard a lot of anecdotal evidence to suggest the performance of an ICF house is better than an 'average' house.  So I'm under-spec'ing the heat pump now and will monitor it's performance over then next year or two, and if we need to bolt on more than we can look at the options then.  It's better than a bigger spend now at a cost of higher heating rates, but even with that it'll still be less than using Oil for a year.  


So - now thats decided, I can stop talking about my pet topic and concentrate on the more mundane items!

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