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In an ideal world every occupied building in Ireland would be energy upgraded to the highest standard, tapping into numerous benefits for the building occupant, the construction industry and society as a whole. Construct Ireland is calling for the introduction of pay as you save, a repayment model which offers the potential of making significant energy upgrade investments achievable in the vast majority of Irish buildings, as Jeff Colley reveals.
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Biobased soy foam insulation still visible prior to air-tighness sealing
The solution is 7m2 of evacuated tube panels, set to be supplied and fitted by CareyGlass Solar just after Construct Ireland’s site visit. Daly explains that he chose evacuated tubes over flat plate panels in order to achieve maximum winter efficiency. “The roof is quite shallow in order to fulfil planning restrictions on height, which gives us a pitch of only 23 degrees.” The optimal pitch for Irish latitudes is closer to 40 degrees. “So we’ve split our solar water system into two banks. We’ll have a roof bank and a wall mounted bank to give us an average of 40 degrees…Between the two, we’ve got a reasonable orientation; it’s slightly geared towards winter, because that’s when we want to maximise solar gains.”
Stephen Smyth of CareyGlass Solar says that the split systems required an advanced solar controller in order to optimise their performance. “One of the reasons why the T12 and T18 systems we’re installing are so efficient is because of the CPC backing on our tubes. This is a compound parabolic concentrator, which concentrates the sun’s radiation levels at fairly diffused angles to the centre of the tube.”
A Dimplex SI 5 ME heat pump with a rated output of 2.7kW fitted by Geothermal Solar provides back-up for space heating and hot water. “What’s different about the heat pump is its size,” says Daly. “It’s small and it’s geared towards hot water, so it’s designed for a higher temperature output.” The heat pump is fed from two separate collectors; a conventional ground array in the back garden and a second in the grey-water tank in the plant room. A sensor in the grey water waste pipe will divert all warm water run-off to the tank where the second collector is located. “The idea is to harvest the warm water and extract the heat. The temperature in the tank could be anything from 20 to 30 degrees, even up to 40 degrees at times, so that increases the coefficient of performance (COP) of the heat pump very significantly from 4.5 to 5 on average.” Based on analysis Daly has carried out, he expects to harvest 2,500 kWh a year from the grey-water system. Current provisional DEAP calculations and ratings exclude this anticipated contribution.
In a further innovation, excess heat generated by the solar thermal array during the summer will be used to charge the ground collector. Surplus hot water is sent to a heat exchanger at the heat pump. The heat pump will effectively go into reverse, bringing the heat out into the soil and storing it there. The logic is that the ground will retain some of that heat through to the winter months, thereby boosting the efficiency of the pump during the heating season. “Even if it’s only a couple of degrees, we will end up having a higher efficiency for a period of time,” says Daly. “This aspect of the project is very experimental; we haven’t modelled or calculated it in detail, but if we get a couple of extra degrees across the ground collector, it would really increase the efficiency of the system in the autumn and winter.”
Hot water is maintained in a 500L dual-coil solar tank. Because the heat pump in the normal course of events will produce 35 degree water only, the heat pump coil is set low in the tank, and is much longer to provide a more generous surface area. Purpose made for the project, the heat pump coil sits outside the solar coil.
The heat pump provides space heating backup through the HRV system rather than radiators or an underfloor network. A liquid heating circuit exchanger in the air supply unit carries the heat to the fresh air supply points throughout the house. The system itself is an Xpelair Xcell 301 unit from Dimpco, also fitted by Geothermal Solar. The ventilation system is also provided with an external subsoil heat exchanger. These are common on the continent in places where air temperatures routinely reach -10 degrees C, and lower during the winter. By drawing air from a ground loop, the system takes advantage of constant year round subsoil temperatures. Daly has installed the loop, but is not going to connect – and incur the fan penalty – until he has thoroughly modelled its functioning in a more temperate climate.
On rendered areas, the external walls are first battened and fixed with Heraclith-BM, a single-layer wood wool slab from Skanda
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Issue 1, Vol 5 Out Now
The new look issue of Construct Ireland is available now. Click here to subscribe online and have the latest issue delivered to your doorstep
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