In 2006 we imported, from Denmark, a Trelleborg "Zero-Energy" House and built it in Devon. It's a timber frame timber clad structure of about 220 m^2. 8m wide by 14 long ish. with the narrow aspect south (thanks planners). Mainly open plan internally downstairs. 4 Bedrooms, 2 bathrooms and a small en-suite lived in by 2 adults, 3 children and a dog.

The house is well insulated, it has 300mm rockwool fibre batts wall insulation. Below the concrete screed is 75mm polystyrene, between the concrete and the timber floor is another 150mm polystyrene. The internal walls and floor voids are filled with rockwool insuation. The room in roof design has insulation of about 200mm ish and then the loft has 300- 450 mm.

The windows are "Rationel" timber framed double glazed units. There are no trickle vents and the house has a MHRV system. This uses about 0.06 kw/hr (60 watts or so) continuously.

The air tightness is not great, with the odd small gap around french doors and windows.

The space heating is provided by an Genvex 0.8kw Exhaust Air Heat Pump, integrated with the MHRV. This extracts from the kitchen area, utility, 1 x downstairs and 2 x upstairs bathrooms. The heat pump then adds extra heat and "warm" air is put into 3 x vents in the lounge, 5 x in bedrooms and 1 on the upstairs landing. There is an additional 1KW electric duct boost heater that I don't use (long story)

A 5kw "Scan" woodburner is in the lounge. The chimney goes through the master bedroom as another heat source. That is an awesome bit of kit.

Each upstairs bathroom has electric underfloor heating timed to provide about 30 mins in the morning and about 45 mins in the evening to take the chill off the tiles. (total of 2.0 Kw)

Water heating is provided by a "Vanvex", this is an air to water heat exchanger of about 0.8kw integrated with a 185 L water tank. It heats to 50c and once a week puts the tank temp to 60c to "disinfect". There is a 1kw immersion heater installed as backup.

The problems:

We have a huge condensation problem. Every bedroom has condensation for 4 or 5 cm up the bottom window pane on any cold night, say 7c or less. If we turn the Genvex down to slow fan speed at night (as recommended for heat efficiency) then every window in the house is wet) so it stays on high (and noisy) speed

The water heating system seems to take for ever (well it's only a small HP). This leads to the strange situation on very cold winter days of the water tank taking 20 hours to recover from 20 to 50c... There is a 1kw immersion heater but then that kind of defeats the objective. Strangely both the vanvex and genvex are located with the air ducting coming in through one side of the house and out through the other. This ductwork runs though the joist void between ground and first floor. So last winter it was sucking in large quantites of -10 air, and putting out similar amounts of -17 air. (cold bridge anyone?)

The Genvex space heating system cannot generate sufficient volumes of warm air to produce an decent temperature in the house. Although the HP can heat the outside air by about 30c, on cold days say zero or below, then the internal temp will be about 15c unless you stand next to the outlet duct at the end of the house the pump is at. The temperature drop along the ductwork is high, in the order of 5 c or more. Some additional insulation work has reduced this but not by much.

The space heating would normally start about mid october, this year we've decided to leave it off as long as possible to save money...so far still no space heating. But the temps are down ... 4c outside gives 15c in the upstairs rooms and about 18c in the lounge. So heating will have to go on shortly.

Add onto this the cost... we use a shade over 10,000 kw/h a year. Some playing around with an Ecoeye reckons that about half is spent on the two heat pumps. So each pump uses about 2,500 kw/h a year. That means each pump is running for an average of about 3,000 hrs a year. (probably less as there is a lot of defrost cycles!)

So what should I be doing. I read somewhere that a domestic heating system should be able to have bedroom temps of 18c and lounge temps of 20?

Is this salvageable or should we rip the stuff out and start again, seriously expensive but I'm fed up with the energy use and the cold! Add onto this the MHRV is quite noisy and as the children get older the house use has changed from where we could light the woodburner and all be in the lounge to where we tend to be in and out more, (scouts, swimming, school etc) so a more automated system would be better.

Any thoughts...

U-values for walls and ceiling? and duct sizes?

You dont need to rip everything out, the ASHP is undersized and can upgraded to something beefier. 0.8Kw seems small.

Is the house orientated and designed to make use of solar gain, lots of glazing on the south side, little on the north etc?

My house is heated entirely be solar gains, incidental losses, light bulbs, people, thermal storage, I have better windows than you and am very air tight (less than one)

I was told that my MHRV would never be capable of transporting enough heat around the house and my ducts start at 200mm then 150 and 125 but it does, utilising a smaller heat pump 300W down to -3C when temp falls to 18C indoors by -6C

I reckon that you should do an airtightness test and rectifications as a first point of call

what are your fan speeds and energy use figures?

Water heating is provided by a "Vanvex", this is an air to water heat exchanger of about 0.8kw integrated with a 185 L water tank.
snip
This leads to the strange situation on very cold winter days of the water tank taking 20 hours to recover from 20 to 50c

Someone check my figures but...

(185 x 30 x 4186) / 20 x 60 x 60 = 322 watts

from an 800W heat pump isn't a great COP. Perhaps worth doing a more accurate test?

Sorry correcting last nights fatigue error, it's a Vanvex 285 V TT for the water.

Thought I recognised this topic..

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=6545

Well that’s embarrassing, I’d completely forgotten about that thread when I sat down in a grump last night to write this one. I knew I'd got involved in a discussion about it on the web before but for some reason thought it was elsewhere...I guess I only get fed up in winter…sorry!

Both systems are independently ducted to the outside world. If I can get digitise the plans slightly I’ll post them.

The system is the Genvex 215l vp-tt running a 520w compressor with 2 fans of 60w each… The vanvex is the 285 l version with the 585w compressor. I know we’ve seen some of this before now! I don’t know the volume of airflow house volume I have at home (still in the office) There is a distinct possibility the ducts have been under sized, the builders have pretty much admitted it as it seems a couple of houses built around the same time (in Denmark) have similar issues. Slip of a pen in the ventilation design office is suspected. Since last winter we’ve had a couple of bits of ceiling down to check and re-lag some of the ductwork. Doesn’t seem to have made a huge difference.

We’ve had the builder round with volume and flow measuring kit repeatedly to balance the system.

Posted By: daysleeperWell that’s embarrassing, I’d completely forgotten about that thread when I sat down in a grump last night to write this one.

Hmm, so has anything changed since then?

It seems to me that in the absence of progress towards a solution, you need to have an expert come and look at the house and its systems. Some of the engineering types in the AECB might be a good place to start looking for one. Check what the specification of everything is supposed to be, why its not working properly (design error, build error, operation error etc), and make a plan to fix it. The plan may include a solicitor, and since the sale of goods rules mention six years somewhere, IIRC, I think you should do it promptly!

daysleeper has already said that the two systems are independently ducted to the outside world, so I don't think the DHW recovery time issue is related to the MVHR. I just want to work out whether the MVHR flow rate is set sufficiently high to manage humidity levels & carry all the available ASHP energy into the house.

David

Posted By: davidfreeboroughdaysleeper has already said that the two systems are independently ducted to the outside world, so I don't think the DHW recovery time issue is related to the MVHR.
David

The DHW is a completely separate system there is no connection between MHRV and DHW.

I just want to work out whether the MVHR flow rate is set sufficiently high to manage humidity levels & carry all the available ASHP energy into the house.

The short answer is no it's not, sort of. The fans run at 75% normally but there seems to be little difference at 100% though going down to 25% results in condensation everywhere including unoccupied rooms.
The builder's already accepted that the system can't push/pull enough air through the house to match the spec. Though they are unsure if that is the reason for the condensation. They "think" the volume problem is because of undersized ducting, though in addition the house is right at the top of the volume range for the machine. The question is what's to be done about it. We'd rather not rip all the walls apart to get at the ducting and running the fans on high at night means the noise in the downstairs bedroom is unacceptably high.

Hmm, so has anything changed since then?

Yes, the acceptance from the builders side that there is a fundamental problem and a few more holes in my ceiling where ducting junctions have been inspected and re-lagged.

How bad is the condensation? Is it running down the windows onto the window sill? Does is evaporate on its own in the morning or does it need to be wiped away? If it's pooling on the window sill then I would say you need to do something about it.

Bad, see photo from last winter.

Can you reduce the amount of water vapour being released in the house? Do you cook on gas? Would you consider moving to a halogen or induction hob? Do you dry washing in the house? Could you put washing outside until it is almost dry & then bring it inside to remove the last few percent of water?

We are fully electric so cook on Induction. There is a washing machine and condensing tumble dryer.

If you've done everything you can to reduce water vapour being released in the house then you need to check that the condensation isn't due to cold spots. Do you notice significant variations in temperature around the house? Does the condensation collect in areas which are colder than others? Can anything be done to increase the temperature in these areas?

Temperature variation around the house is a problem, but particularly the bedrooms where we suffer the worst condensation are the coldest rooms.

Once you've been through these options then you're left with increasing the ventilation rate &/or the distribution of heat coming from the MVHR unit. Has the MVHR unit been properly commissioned, i.e. has the flow been checked & adjusted at each extract/inlet vent?

The installer has been round and round and round rebalancing and setting up.

Is the temperature drop along the ducting within specification? Are all of the ducts lagged with at least 50mm mineral wool? Is the pressure drop along the ducting within specification? Is all of the ducting low loss rigid ducting, or do you have some flexible ducting?

Temp drop has been out of spec, thus the extra work re-lagging. Pressure drop seems ok but the overall pressure is low, all the ducts are rigid and sit in insulation, but how thick that is I'm not sure.

If you can get answers to these questions then you can decide whether to reject the MVHR unit as not performing to specification &/or reject the builders installation as not fit for purpose.

David

Well new fans and software coming next week. Not convinced and I suspect neither is the UK rep.

Thanks Paul,

It's worse than that, the ASHP input is only 520w !

If we use the woodburner in anything other than arctic conditions then the lounge rapidly goes from conditions needing 2 overcoats to wearing shorts. Seriously the woodburner punches the temperature in the lounge up to about 25c very quickly even in cold weather, problem is that heat does not travel. The nearest intake point for the MHRV is about 7 meters away and with all the internal walls insulated there isn't much appreciable difference. The bedroom above gains a few degrees from the internal chimney.

We used to use the woodburner more, like fire it up in the morning and keep it going for a few hours then again at sunset till bedtime. However, as the children have started school, and we are in and out more it has become only a weekend late afternoon/evening thing.

If a simply solution is what you are looking for, try reducing the load on the heating system. Your woodburner seems to have more KWs output than needed, have you thought about a back boiler on the woodburner (and / or another woodburner) and link in a few rads to it to one side of the house. That means you could focus the heat output to a smaller area, thus more efficent, less noise and more heat.

Only a thought.

I would say also, 10,000kw per annum for a 220 sq m house - is that just space heating, space heating and water heating or all energy.

Most normal houses usually need to throw 15,000 - 20,000kw for energy costs to a family home

RR