mvhr and minimal other heating

[scottishjohn]

doing some reading it would appear ,if you believe  the hype, that a passiv house can do without UFH

I find this hard to believe and would welcome all views  on this subject 

my thoughts at this early stage are to fit UFH pipes to slab anyway -at least .

I have even read that next year there will be  a graphene heater element that will work with tessla power wall and solar Pv --

that too sounds a little star trekish 

 

[Crofter]

Well it's pretty much the whole point of passive house design.

There is a great deal of 'waste' heat given off by your hot water system, as well as fridges, and even the occupants of the house. So the idea is that you insulate the house to the point where it only needs this background heat input to achieve an appropriate temperature. There's also solar gain to consider.

 

It's not MVHR as such that allows this- it's more down to the level of insulation, and not having oodles of windows (even the best windows lose heat at three times the rate of a standard wall).

[Onoff]

No vested interest here whatsoever but I can confirm, having visited @PeterStarck's house that UFH is not really required. Might have something to do with his meticulous attention to detail on the build where it counts and the fact his air tightness beats the regs by a factor of something like x4. The sprayed icynene insulation too.

 

 

[Gone West]

@scottishjohn We don't have UFH and use electric towel rails in the bathrooms as our main source of heat. We also have warm air through the MVHR system. The U factor for PH walls and roof has to be less than 0.15W/m2K. The U factor for my walls and roof are 0.095W/m2K, which along with good airtightness, is what contributes to the fact that I don't need UFH . I live in the south of England near the coast which is another reason I can keep my house warm without UFH. I found it very useful to play around with the PHPP using different U factors, glazing and weather data to come up with the the best wall and roof construction. My blog has all the gory details. Good luck with your project.

[Onoff]

1 minute ago, PeterStarck said:

@scottishjohn We don't have UFH and use electric towel rails in the bathrooms as our main source of heat. We also have warm air through the MVHR system. The U factor for PH walls and roof has to be less than 0.15W/m2K. The U factor for my walls and roof are 0.095W/m2K, which along with good airtightness, is what contributes to the fact that I don't need UFH . I live in the south of England near the coast which is another reason I can keep my house warm without UFH. I found it very useful to play around with the PHPP using different U factors, glazing and weather data to come up with the the best wall and roof construction. My blog has all the gory details. Good luck with your project.

 

I forgot @scottishjohn was in the Arctic!

 

Out of interest how would your build fare up North? At what point doesn't it "work"?

[Gone West]

Just now, Onoff said:

 

I forgot @scottishjohn was in the Arctic!

 

Out of interest how would your build fare up North? At what point doesn't it "work"?

Quite honestly I don't know because I only used weather data for this site. It would depend on the general weather data for the area and the openness of the site.

[newhome]

I don’t have a passive house but I have UFH both upstairs and downstairs. I wouldn’t have it upstairs again out of choice. @PeterStarck is an exception I think as most people with houses built to passive standards seem to fit UFH downstairs although towel rads for upstairs seem quite popular. Living where you do I think it’s a no brainer to fit UFH pipes in the slab at least. 

[readiescards]

8 hours ago, scottishjohn said:

 

I have even read that next year there will be  a graphene heater element that will work with tessla power wall and solar Pv --

that too sounds a little star trekish 

 

 

Ooo, send us the link please

Edited November 12, 2018 by readiescards

[Onoff]

21 minutes ago, PeterStarck said:

Quite honestly I don't know because I only used weather data for this site. It would depend on the general weather data for the area and the openness of the site.

 

Fair enough. Was there a minimum ambient temperature allowed for in the design?

[Jeremy Harris]

8 hours ago, scottishjohn said:

doing some reading it would appear ,if you believe  the hype, that a passiv house can do without UFH

I find this hard to believe and would welcome all views  on this subject 

my thoughts at this early stage are to fit UFH pipes to slab anyway -at least .

I have even read that next year there will be  a graphene heater element that will work with tessla power wall and solar Pv --

that too sounds a little star trekish 

 

 

PassivHaus has never been about having no heating, for several very good reasons, not least of which is that if you built to a "no heat input ever required" standard then the house would almost certainly need a fair bit of cooling in warm weather.  We don't like the house to be warmer than about 24 deg C, and with the level of insulation and airtightness we have (similar to @PeterStarck, although not certified as a PassivHaus) we have found that cooling can be an issue at times.  Over the past couple of years we've had days when the outside air temperature has been higher than we'd like the house to be, so opening windows just makes the house warmer.

 

The choice of heating system is really down to personal preference.  We have an MVHR that has a built-in air-to-air heat pump, and that has enough heating capacity to keep the house warm in winter, but I don't much like the "feel" of warm air heating, so we don't use the MVHR in heating mode, only in cooling mode in hot weather (the heat pump is reversible so will cool the air as well as heating it).  We had UFH pipes cast into our passive slab as a part of the package, so we heat and cool the slab with a small ASHP.  We find that the very small heat output from the UFH gives a comfortable feel that we both prefer, but that is just a personal preference.  The heat input needed even in really cold weather is tiny, so the UFH never makes the floor warmer than about 23 deg C, if that.  We also have heated towel rails in the bathrooms, and they have to be on a timer I've found, as otherwise they tend to make the bathrooms too warm.

 

Local climate makes a very significant difference to the heating and cooling requirements of a house that's built to passive standards, and I found that we accidentally created a significantly warmer micro-climate around our house as we had to cut back deeply into a hillside at the bottom of a valley to get a level plot, and that's had the effect of providing a lot of shelter from the wind, so we have an air temperature around the house that's normally 1 or 2 degrees warmer than the local weather data suggests.  The effect of this was to seriously screw up the PHPP over heating risk prediction, which then meant having to add external solar reflective film to help keep the sun's heat out in Spring and Autumn (we have overhanging shading to deal with the summer sun, but that doesn't work for low sun angles).

 

The most important factor when looking at construction methods for a low energy house is, IMHO, making sure that the wall and roof construction method provides a high decrement delay, so that the house has a long thermal time constant.  Once the decrement delay exceeds the time that the sun is likely to shine on a surface, say 6 to 8 hours, then the risk that radiant heat will be conducted through the walls and roof to the interior reduces a great deal.  Decrement delay is a function of both the thermal resistance and the heat capacity of the structure.  Having a low U value structure with a low heat capacity will give a short decrement delay, so it's important to consider this carefully.  Finally, wind has a pretty large impact on heat loss, and this becomes more noticeable as you decrease the overall heating requirement, to the point where wind speed around the house may be as important as the air temperature in determining the heat input required during the heating season.

[Onoff]

2 minutes ago, readiescards said:

 

Ooo, send us the link please

 

There was graphene paint a few years back to supposedly be used as a heating element on walls. 

[Ed Davies]

AFAICS, Passivhaus and UFH are two quite separate issues: a Passivhaus should need very little heating to the point where UFH is not needed, after all the idea is that you can heat it just by heating the supply air from the MVHR so a couple of electric convector heaters or towel rails should do. In a way fitting UFH is an admission of lack of confidence.

 

However, there are two reasons you might choose to use UFH. One is that it's a pleasant way to heat the house and likely reasonably efficient as its radiant heat probably allows a slightly lower indoor air temperature which will reduce the (already small) ventilation heat losses a bit.

 

The other is that it's a good way of using the output of an ASHP as it allows the heat pump to operate at a much lower temperature than it would with, for example, radiators so it'll operate more efficiently. Whether it's worth having an ASHP purely for space heating in a Passivhaus is debatable (there are a few on here who choose to only heat with direct electrical resistance heating) but as you also need DHW it's much more likely worthwhile. Still not absolutely clear cut, though.

 

AFAICS - as far as I can see.

UFH - underfloor heating.

MVHR - mechanical ventilation with heat recovery.

ASHP - air source heat pump.

DHW - domestic hot water.

[joe90]

@JSHarris is right about local weather conditions, we are the opposite to him, we have almost constant SW winds from the coast and I believe it impacts on our heat requirement .we are very near passive hous insulation and airtightness but ASHP and UFH are needed to provide affordable heating and DHW as we have no mains gas.

[Guest Alphonsox]

We're sat on a peninsula set out in the Irish sea and definetely require heating despite a Passive-ish build. The cooling effect of the near constant wind is significant. Whether you go for UFH is a matter of personal choice, however installing the UFH pipeing is a very cheap thing to do at the build stage and expensive to do as a retrofit. We installed the UFH ourselves at a cost of a few hundred quid and currently run the heating from E7 electricity via a 3Kw immersion heater - Whole house heating doesn't come much cheaper.

[ToughButterCup]

This thread -so far-  is a good precis  of  UFH and PH ideas. I wish that a few years ago we'd had a thread that summarised issues so well.

 

I suggest we pin it.

[lizzie]

Like others I am passivish but need UFH. We are on top of a ridge and exposed, lots of wind.  Would not want to be without the UFH even with MVHR and heated towel rails.

[ToughButterCup]

But @lizzie, wimmin are always '... freezing... ' ........

[lizzie]

6 minutes ago, recoveringacademic said:

But @lizzie, wimmin are always '... freezing... ' ........

You are right of course?

[Stones]

34 minutes ago, Ed Davies said:

AFAICS, Passivhaus and UFH are two quite separate issues: a Passivhaus should need very little heating to the point where UFH is not needed, after all the idea is that you can heat it just by heating the supply air from the MVHR so a couple of electric convector heaters or towel rails should do. 

 

+1.  My understanding was the original PH standard was set at the level it is, because it was possible to provide such limited heating via an electrical heater in the MVHR, i.e. no requirement for a full CH system.  It does not mean no heating is required.

 

As referenced, there are many factors which will impact on your heating requirement.  We live in an exposed position where wind, rather than low temperature is the main heat loss driver.  In addition, our house is 'n' shaped, increasing the surface wall area exposed to the elements which drive that heat loss.

 

One of my colleagues built a house using the same ICF system as us, but opted to forgo UFH, relying instead on a post heater in the MVHR and 4 oil filled radiators spread between key rooms.  The temperature differential room to room is quite noticeable.  He has been honest enough to say that he regrets not fitting UFH, if for no other reason than comfort. 

[Nickfromwales]

If you’re going to the efforts of building your home to such a good standard, what a bag-o-crap it must be to litter it with £30 heaters you ran out to get from Argos when your wife told you “I told you ‘“   

UFH is the number one way to heat imo, and in conjunction with a decent slab ( as opposed to a thin screed ) you can realistically plan for fine tuning your heat input to the nearest 0.5 degree. 

 

Heating by duct ( given it also commands a much higher airflow rate ) would be the last option for me to look at tbh as a generic MVHR should be near inaudible and unnoticeable in operation, and to use it for heating in anything other than a ‘small’ dwelling would take you away from that target. 

Accepting that higher flow rates are necessary, when cooling is utilised, is easy  when you compare it to the rather unsympathetic alternatives ( split aircon ) etc. 

 

[pulhamdown]

If you are building in Scotland, putting UFH pipes in an insulated slab is a no brainer.  Then you at least have the option to use it if you need it.  We are in eastern Scotland, and have a near passif standard house, and quite exposed.  Our internal temperature rarely drops by more than one degree overnight, and even then, the UFH brings the temp back up quickly.  We face SE, and rarely get overheating, so from my point of view we have got the insulation / overheating balance about right.  But read @J S Harris's post above really carefully.  He sums up the situation in a nutshell.  I'd second pinning this thread.

 

Edited November 12, 2018 by pulhamdown

[Pete]

1 hour ago, Alphonsox said:

We're sat on a peninsula set out in the Irish sea and definetely require heating despite a Passive-ish build. The cooling effect of the near constant wind is significant. Whether you go for UFH is a matter of personal choice, however installing the UFH pipeing is a very cheap thing to do at the build stage and expensive to do as a retrofit. We installed the UFH ourselves at a cost of a few hundred quid and currently run the heating from E7 electricity via a 3Kw immersion heater - Whole house heating doesn't come much cheaper.

Can you give details of how much your elec bills are to heat your house and how often you have to have the heating on if the weather is fairly consistent outside. T

[joe90]

1 hour ago, Nickfromwales said:

what a bag-o-crap it must be to litter it with £30 heaters

 

Yes, but, this is my back up for our bedroom if the weather is very cold for the odd couple of weeks in the winter. I did not want to go to the expense and work of UFH upstairs Just in case it got that cold occasionally. I bought a slimline 500watt heater that lives In a wardrobe that I can plug In fir an hour or so. I have wired for a post heater in the MVHR but not sure of its effectiveness.

[scottishjohn]

you have basically confirmed my thoughts --fit ufh in good insulated slab anyway ,
our climate here is very similar to cornwall --continuos spring  interspersed with a bit of cold and heat #

over heating --wife will soon sort that that -she is a window opening freak .

so sounds like smallest ashp you can get --3kw  will kill the job .

Or i might go for solar thermal as ihave had until recentely 2x20 thewrmoax evac tubes onroof of present house 

20years ago idi a retro fit underfloor system in this house by routing all  chip board floors ,then coveringwith 6mm ply

it has workeed well and solar actually contribute to space heating as well as the hot water#

downside was storage tnak not large enough at 300litres so in summer it sometimes looked like a steam engine .

kit i got then was crap --not the tubes ,but all other bits ,like plastic air separator unit --yes it melted and  so did the panel sensor 

rersult so much heat that the plastic insulation melted off the copper pipes --so thats 170c + for sure .

maybe will do what I always wanted and use to .solar thermal and large tank if heating load is as low as you say .

the day I finished the installation was  in february --i turned off lpg boiler and on a good sunny day it would run UFH att 25c + lifting tank to 50c

so maybe my nutty professor idea of a 5000 or10000litre concrete tank insulated to death  on outside could be a winner

will wait to see final heat clacs when house is fully designed  to make decisons --evactube panels are half price of what they were so i could have twice the are for same price 

[le-cerveau]

Our Pasive Style (not evaluate house) is currently drawing less than 0.5Wm² to maintain an internal temperature of 21^oC with the outside running between 7 and 10^oC.

 

I can make a fairly accurate estimate at the moment as the house is unoccupied and the DHW shut down (so no losses there), the ASHP is firing up about every 36 hours to re-charge the PCM34 SunAmps and drawing an average of 2.3kWh.  Assuming a CoP of approximately 3 (will check details when next there) gives 7kWh every 36 hours giving 194W per hour, spread over a house with over 400m² floor area, gives less than 0.5Wm^2.  The MVHR is ticking over and everything else shut down, Fridge running, one computer (other reasons of remote access) and the network equipment in the attic (inside envelope).

 

We have UFH throughout as a unified temperature, upstairs runs about 1-2^oC cooler than downstairs so it is fine for us.