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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorjohnuready
    • CommentTimeJul 14th 2018
    My passive bungalow works extremely well but as the utility room is in the centre of the property it can get too warm. The utility room has the MVHR, PV inverter, hot water tanks and all the bits of electronics that manage and control the property. I was thinking that I could spur into MVHR pipe to the outside world and extract heat directly from the utility room with an extraction fan that is thermostat controlled

    Anybody have any ideas or solved direct extraction in a passive building?
    • CommentAuthortony
    • CommentTimeJul 14th 2018
    In very hot weather, yes but presumably in tthe winter you can use the heat in the house.
    Posted By: johnureadyI was thinking that I could spur into MVHR pipe to the outside world and extract heat directly from the utility room with an extraction fan that is thermostat controlled

    Is that spurred into the outboard side of the MVHR? If so then heat will be lost in the winter. If you have a summer bypass then if it is spurred to the inboard side then the heat will be saved in the winter. Otherwise switch off the fan in the winter and leave the door open a bit.

    From where in the main is the excess heat coming? I suspect the hot water tanks and associated pipes, if so then more insulation on the tanks and pipes would be a better solution to dumping the heat outside
    • CommentAuthorjohnuready
    • CommentTimeJul 15th 2018
    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?
    • CommentAuthorSilky
    • CommentTimeJul 15th 2018 edited
    maybe a small internal heat pump that cools the house and dumps the heat into a well insulated hot water tank, if you could justify that the cost of running the heat pump would save you money in comparison to your existing water heating method + air con

    edit: just a clarification, this is the type of heat pump that directly cools the air inside the house (nothing to do with running cold water through UFH), the cost is around 2K and if used for only a few months of the year then the equipment should last a lifetime. The issue could be an excess of hot water / duplication of hot water production when there is already solar DHW. But I would guess this is still a cheap way to cool the house down. It would work better if applicances such as washing machine, dish washer, shower can use preheated water

    edit : example link
    • CommentAuthorgoodevans
    • CommentTimeJul 15th 2018 edited
    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.
    • CommentAuthorjohnuready
    • CommentTimeJul 15th 2018
    Goodevans - the temperatures currently showing is with the house empty for two weeks with no windows or doors open and no portable high speed fan taking the heat down in the evening by cooling the fabric, front door to back. The solar gain from a lot of glass works against me in the summer but helps in the cooler months. Perhaps the answer is a split AC unit in the kitchen day room. It’s running cost would be £0 during the summer, Immersun and PV installed. I would assume they as a split unit runs internally the balance of the MVHR would not be upset?
    • CommentTimeJul 15th 2018
    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?
    • CommentAuthorjohnuready
    • CommentTimeJul 15th 2018
    My summer bypass closes ok and has a varaiable temperature set point. What temperature do others have the bypass set to?

    The PHPP was ok with the amount of glass but the level of insulation went up when I installed a service void with space blanket on all outside walls.

    The property is a buglaow so no stack effect.

    The portable fan I find effective in the evening when I’m home to reduce the temperature of the building by blowing the heat out ready for the next day.

    The utility room does not have an extract vent, now that could be next job.

    The utility room has the PV inverter, Immersun and Immersion heaters in the tank, Solar Themal hardware, hot water tank and MVHR. The PV Inverter this time of year puts out a lot of heat. Shame it’s too late to put the inverter in the garage.

    As my winter heating is very low, the AC split unit would be a cost effective way to reduce the temperature in the summer and a cheap way to add heat in the winter. No Gas just Electricity to the property.
    • CommentAuthorgoodevans
    • CommentTimeJul 15th 2018
    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.
    • CommentAuthorgoodevans
    • CommentTimeJul 15th 2018
    For summer shading pay most attention to the east and west windows - these windows let in the most heat in the summer.
    • CommentTimeJul 15th 2018
    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 :shamed: )

    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.
    • CommentAuthorjohnuready
    • CommentTimeJul 16th 2018 edited
    The bungalow is in the UK

    I have no wet UFH just electric underfloor heating mat in the bathrooms, only used when it gets cold.

    The kitchen day room has 12sqm of south facing glass and 7sqm of the east facing glass.All the glass have thin mesh curtains that are not as effective at keeping the room cool as 8sqm of east facing glass in the lounge with heavy duty curtains.

    Yesterday I was looking at battery operated blinds ok but costly. I have found good quality AC split units that are not that expensive and with the benefit of £0 to run in the summer and extra heating on demand in the winter at the equivalent of gas costs I think I need to test out a split for next year.
    • CommentAuthorRobL
    • CommentTimeJul 16th 2018
    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.
    • CommentAuthorjohnuready
    • CommentTimeJul 16th 2018

    I have exactly the same unit. When I get home I’ll check my settings.

    I have checked the efficiency of my SMA Inverter at 97% in the summertime I can produce 25kw per day that’s a lot of heat that goes nowhere. Should have installed the inverter in the garage and oversized the cables. Perhaps move into my cold roof space just above and the utility room.
    • CommentAuthorjohnuready
    • CommentTimeJul 16th 2018
    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?
    • CommentTimeJul 16th 2018
    Assuming you mean 25 kWh generated per day, then if the inverter is operating at 97% it will be putting 25 x 3% = 0.75 kWh of heat into your utility room. (if that's what the efficiency number means, I don't know). Which corresponds to a continuous power of 0.75/24 kW = 31 W. So not a great deal really. It seems likely your DHW tank is putting a lot more than that into the room.
    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.
    • CommentAuthorgoodevans
    • CommentTimeJul 16th 2018
    I agree with Peter - I think the heat will be coming from the hot water tank and pipes - especially if the immersun is heating the water to v high temperatures. But note that the the room is only about 7 deg C hotter than the surrounding rooms.

    Other Ideas - Perhaps in summer limit the temperature of the DHW.

    Overall however the heat coming in via the glass is the core problem - get blinds/shutters/shades external to the glass. Once the heat as made it through the glass it's much more difficult to remove (particularly with the insulation levels you have achieved.
    • CommentAuthorjohnuready
    • CommentTimeJul 18th 2018
    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.
    • CommentAuthorjohnuready
    • CommentTimeJul 18th 2018
    Looking deeper into the overnight numbers with the outside temperature dropping to 15 last night the bungalow only drops 3 degrees overnight with a slow build up of heat as the sun pushes through the glass. I’ll check the MVHR settings on my return.
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