Domestic Cooling Systems

bemak

Given the current regulation for new-builds in terms of insulation, air-tightness etc, a knock-on effect has been overheating due to solar gain which is becoming a big problem, particularly when you have a lot of glazing. If glazing is specified correctly (low-e) etc the effects can be somewhat mitigated but you're inevitably going to have issues.

One option is HVAC - which is a step up from MHRV in that it provides air conditioning. This can be done through integrated vents or individual stand-alone units (which look very commercial).

I was reading recently that radiant ceilings are starting to appear in domestic projects. For anyone that doesn't know what a radiant ceiling is, it's basically like underfloor heating except it's in the ceiling - and it uses cold water instead of warm water to provide cooling. I'm not convinced by this approach as I think you might inevitably start to get issues with condensation if the temperature in the ceiling drops too low. (dew point etc)

So I was wondering what systems people have put in place recently that have worked well to broaden my understanding of the possible solutions available.

mike_2009

If you want to design out overheating, have the new build designed to passive house standards - the PHPP software can reduce this risk tremendously. Plus in Ireland it's not very often we have heatwaves where this is an issue. If your house design puts a lot of glass on the south facing side however to take advantage of views / light, you've a design tradeoff here.

As for mitigation - on the continent they use external roller shutters to control this and prevent light hitting the glass in the first place. They can be half closed, closed with holes still allowing some light in or fully closed where those holes then disappear to blacken the room. Motorised or manual, you've probably seen them on your holidays. I'm finding it hard to get a supplier in Ireland / who ships to Ireland though. The alternative is briese soleil which deal with the high summer sun and don't get in the way during the low winter sun when you want solar gain. Wooden or Aluminium ones are available.

An Air to Air Heat Pump is sometimes a good addition - there are units being developed which also provide hot water for apartments etc but these provide useful heating and cooling as needed. An air to water heat pump - some units can modulate and provide under floor cooling or just pump fluid around to transfer heat from the floor of very warm rooms where sunlight is hitting the floor, to other areas of the house, helping to balance the heat throughout the house a bit.

I did read of the use of Aerogel/Hydrogel or something like that to absorb excess heat during the day and release it at night. And back to design, those old New Orleans houses with overhangs and open doors / windows to allow a breeze though were very effective back in the day. Having skylights you can open along with ground floor windows creates a chimney effect to cool down (passive stack) the building in the evening when the outside temperature is cooler.

I'm designing to Passive house principals and hope to have an ASHP that can also cool, several velux skylights to cool down in the evening and I'm trying to find a supplier of external shutters so I can integrate them into the window openings at build. I also have Briese Soleil incorporated into the PHPP calculations. My overheating risk is 1% currently but if the climate data is changed to London it increases to 13% which is where we might be headed someday. Therefore active measures may be needed at that point. And a big swimming pool out the back garden!

bemak

Thanks Mike - the ASHP might be a good way to help contribute to cooling. I was speaking to a few manufacturers and one suggested piping in an element to the MVHR system that a heat pump could cool to help reduce the heat of external air before being brought in. He didn't say that it was a particular system - just an idea he had and I think it might have some merit.

The issue with Air to Water cooling slabs comes back to the potential for condensation again. I think you'd have to maintain a temp of at least 16 degrees to avoid it.

At least with blinds & brise soleil, they can be added after if the solar gain couldn't be designed out.

Are you going with ASHP only or have you an AWHP as well? The idea of a second smaller ASHP for cooling is probably the most effective in terms of comfort levels - nice to feel the cold air as opposed to the cold floor. It's great that they can contribute to heating them as well when required although I think I'd still prefer to have rads and UFH as the main source of heating in addition.

mike_2009

The problem of using MVHR for cooling is the heat load in air is very low and the flow rates won't impact the temperatures internally that much. Unless you really crank it up but that only worsens the heat exchange (bringing in more outside hot air to cool down) than your system may be able to cope with. Anyway, I've seen cooling options but the MVHR systems aren't the best carrier from what I've read on discussions elsewhere.

I'll just go with an Air to Water heat pump and underfloor heating on the ground floor. Daikan do convector units for the upstairs off this that I'llalso consider. Otherwise I'd prefer to get A2A with 3 inside units off the same external compressor (much cheaper than A2W) but need a way to heat water which is the main load and BER won't allow just immersion so the A2W heat pump ticks that box. Can't sign off without it!

bemak

The A2A units don't look great though - is there any potential to duct the first floor so that you can have a nice grille on the wall as opposed to the unit? I think that would be my preference