In very hot weather, yes but presumably in tthe winter you can use the heat in the house.

As yet I have not connected anything external to the installed MVHR just thinking about the answer to warm utility room. The utility room has a freezer, solar thermal hardware, one of my two tanks, PV inverter, routers etc. As you can see in my management report today it’s warm in the utility room. The house has not been lived in for the last two weeks but the PV inverter has been very busy. The house idles on 450w per hour and is very highly insulated.

In the summer if it gets too hot I would open the main entry door and use a big powerful fan to suck air through the house and out the lounge patio door.

The house is currently running with summer bypass working.

My thought was to suck air from the utility room in the centre of the house to the outside in summer only.

My other thought was to purchase an offer shelf mobile A/C unit and plug the exhaust into a similar set up that could be sealed during the winter.

Anybody have ideas?

Hmmm - for a pasivehouse all your rooms seem very hot. Unless there is a massive solar gain I think you may be able to do better.

Do you have a manual summer bypass - if so turn it OFF in the morning (or to be more precise - when it is hotter outside than inside) and at the same time close all your doors and windows. In this way you will be using the mvhr heat exchanger in reverse - cooling the hot outside air using the cool internal extracted air.

In the evening (or to be more precise when it is cooler outside than inside) turn on the summer bypass and open all the doors and windows. Use the cool air to cool down the contents of your house as much as possible ready for the next day.

If solar gain is an issue find ways of shading the windows on the outside.

If the internal utility/service room is always getting hot a supply port or an extract port to the mvhr will help a bit - but only a bit - if set to 8 litres per second you could move approx 40 watts with a 5 degree temperature difference.

It's a leap of faith but on hot days keep the house cool by not letting the hot air in - First thing in the morning look at the predicted maximum temperature - if is going to be a scorcher close all the doors and windows and preserve your cool interior before the outside air gets too hot.

Don't mess up your MVHR balance -don't extract or pull in any air except through the MVHR.

If you treat hot outside air in the summer in a similar way to the way you treat cold outside air in winter you ought to keep your house near to the night-time outside temperature all day long.

Posted By: johnureadyIn the summer if it gets too hot I would open the main entry door and use a big powerful fan to suck air through the house and out the lounge patio door.

The house is currently running with summer bypass working.

If it gets too hot, then its hotter outside than inside, so our summer bypass closes. What goodevans says. What does PHPP have to say about what to expect?

A big fan is not needed. Either the wind will drive air from one side of the house to the other, or the stack effect will drive it from downstairs through upstairs windows.

Does the utility have an MVHR extract terminal?

OK first check - are you UK based? I'm assuming so but the EST label on the diagram has me doubting that.

Assuming MVHR bypass is automatic and working correctly then I think the root problem is solar gain. For me I'd be looking at cooling the whole house not just the utility. If the house is closed up night and day the glass lets in the heat during the day with no easy way for the heat to get out during the night - after several days this would be a problem.

Can be fixed by using the excess PV to cool the whole house with a split ac unit or two or, for a cheaper capital option, shading windows externally with temporary screens/films or shutters, awnings or trees.

If you have an ASHP and UFH it may be possible to use that to pump cool water (at 18 deg C or so) through the floors.

When you are away leave the utility door open - the heat in there makes it out to the rest of the house fairly quickly - so best not to let the room get too hot and shorten the life of your electrics. I don't think tweaking the MVHR will be that effective.

Posted By: goodevansFor summer shading pay most attention to the east and west windows - these windows let in the most heat in the summer.

Only if you assume that the south-facing windows are properly shaded. It's the difficulty of shading west and east facing windows, which face low altitude sun, that makes them problematic. There's a lot more energy admitted through unshaded south-facing windows. (I know, I still haven't got around to shading ours in the dining room and living room )

Posted By: johnureadyThe utility room does not have an extract vent, now that could be next job.

I would certainly do that before anything else, although I wouldn't guarantee that it would fix the problem entirely.

The difficulty I see with using an ASHP for cooling is the cost - capital plus maintenance & replacement.

Hi John
Our MVHR (vent axia sentinel+BH) is set in the summer to 18C bypass. In the winter I change the bypass to 23C. I move the temp up & down once a year, just to ensure it always cools if helpful in summer and never bypasses the heating in winter.

There's an outdoor setting too, I set that to 5C - below this number stops the bypass if its cold outside, even though cooling would help - it's to prevent cold draughts.

We haven't got a passivehouse, but I do plan on lots of EWI next year. I'm going to extend the south roof overhang to reduce upstairs Summer heating, and similarly plan to reduce solar gain of our lounge window.

Can anybody check out my thoughts on the 4kw sma Inverter on good day producing max about 25kw, what’s the heat output into the utility room 2.5m x 3m x 2.3m?

Beg, borrow, steal or as a last resort buy an IR thermometer and check to see where the heat is coming from.
I'm with djh, the hot water tanks (and pipes) would be my first choice of culprit.

The bungalow has now not been lived in for 3 weeks with the Immersun off but I left the solar thermal working with the tank keeping at 65. With that and the PV Inverter the utility room is consistently 6 to 8 degrees higher then the kitchen day room with door open. It must as suggested be the glass causing the main problem with the MVHR unable to drop the temperature over night significantly. When I’m home on these very hot days outside I purge the heat by blowing the hot air out at night.

I think the answer is to check all the tank pipe insulation and then think about a split AC unit to take some of the heat out of the buildings fabric on these very warm days. Although it will not be many more months before the glass and high insulation comes in handy.

Thanks for your help.