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This post covers more than just MVHR, but I wasn't quite sure where this post would be best placed. Admins feel free to relocate if need be!

 

As you can probably guess by this post going up late on a Saturday, I've been doing a lot of modelling of our heating and energy systems for our house. It has taken a while to get the model to accurately reflect reality, but I think we've finally nailed it.

 

Whilst not surprising, what it has clearly established is that:

  1. PV is a no brainier, provided you have the capital up front! Though that's another topic all together (posted here).
  2. The MVHR bypass will be insufficient to counter the solar gain during the peak summer months. 

 

It's often said that the biggest problem with passive houses (or near passive as our's is) isn't the heating, but the cooling. They're right!

 

Thankfully we have opening windows and plans to use a canvas above our pergola to shade some of the southern windows. 

 

So more our of general curiosity, what else have people done to keep the tempretures stable and comfortable during the summer months?

 

 

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Edited by Visti
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1 minute ago, Nickfromwales said:

First question, have you read ( Jeremy's for one ) info re solar reflective coatings for the problematic glazed sections? 

 

No, I wasn't aware of that topic. You have a handy link Nick? 

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A brine heat exchange ground loop might be worth considering.

 

I wish I had the land to bury 100m of pipe but I just can't fit it in unless it goes partly under the slab which I've dismissed as a foolish idea but can't get it out of my head! 

 

Your architect @Visti has also installed this system on his new build and there is a brief YouTube video where he chats about it.

 

 

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We just reverse our heat pump to cool the floor, much, much easier to do than plumb in a brine loop, and cheap, just add one extra thermostat.  All air to water heat pumps are reversible, they have to be in order to defrost.

 

However, the best solution is to keep the heat out with external shading, external blinds etc.  Summer is not the worst case for us, it's low angle sun around this time of the year and in autumn, when the sun can get under the shading and deep into the house, so external blinds or movable external shading seems a better thing to try and do, and something I wish we've been allowed to do by the planners.  Getting rid of heat once it is in the house is really a last resort, and it seems better to try and stop it getting in in the first place.

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The guys that made our windows has a glass technician and when I mentioned our phase two conservatory he can supply coated solar reflective glass to cut solar input, I will concentrate on this when phase one is complete ( we move in!!!) which hopefully will be in about a months time?

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My personal view is that the idea of using massive loops of buried pipe for cooling is barking mad.  It would cost more than a cheap air-to-air cooler, would cost a small fortune in ecologically approved antifreeze/inhibitor and overall there would be little, if any,  saving over the whole life cost.

 

If someone already had UFH plus an ASHP then it's a doddle to just switch it to cooling mode, accepting that almost all units sold in the UK will have this mode well-hidden, because if MCS approved for RHI they are supposed not to allow cooling.

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Interesting that the unit Charlie was talking about had a co monitor to up the fan speed if the air got “ stale”, I suggested this a long time ago during my planning stage but thoughts were generally that it was not needed. I still think I would rather the MVHR switched on if the building required it, and not running 24/7, a bit like a room stat for central heating! I know fir a fact that er indoors will be opening windows on sunny days, it’s in her DNA.

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9 minutes ago, joe90 said:

Interesting that the unit Charlie was talking about had a co monitor to up the fan speed if the air got “ stale”, I suggested this a long time ago during my planning stage but thoughts were generally that it was not needed. I still think I would rather the MVHR switched on if the building required it, and not running 24/7, a bit like a room stat for central heating! I know fir a fact that er indoors will be opening windows on sunny days, it’s in her DNA.

 

 

It's easy enough to do, but not sure if there's an off-the-shelf product that will do it.  You can either sense relative humidity (not great as an indicator in my experience - too much seasonal variation) or sense CO2.  The latter is far better and a lot more reliable.  Just set the MVHR to come on if the CO2 concentration exceeds a set limit, say 500ppm or so, then stay on unless the CO2 concentration drops below about 450ppm.  It will normally sit at around 400 to 450 ppm with either the MVHR on or the house empty.

 

I'm not sure if you can buy a controller to do this, but I had thought of building one, as my house monitoring system already monitors CO2 level anyway, so it would be pretty simply to just pull that data out and use it to control the MVHR.  Not a practical solution for you, though, unfortunately.................

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If I remember correctly I got a RH sensor ( or there is one in the unit already) ( it’s been such a long process I can’t remember?), but I do fancy a CO2 sensor, it’s just not on my “to do list “yet.

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Our old mate @DamonHD monitored a school (think he borrowed @JSHarris, monitor), when I looked at his data, there was a pretty good correlation between RH and CO2.

CO2 has to be really high to become a real problem, RH control would probably be better and you can do that though the MVHR to a certain extent.  Just up/down the temperature with a post heater/cooler.

Edited by Nickfromwales
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