MBC timber frame heating advice

[Heppy]

Hi we need some urgent advice about heating our MBC new build house. Basically we are having the slab done at the beginning of Nov and we are getting conflicting advice as to whether we need heating upstairs. We are building a modest 180 sqm three bed house, triple glazed windows, air source heat pump, underfloor heating and a MVHR with solar pv's on the roof. We have been advised my MBC we won't require heating upstairs only electric heated towel rails but Earth Save Products have emailed saying the following. Any advice would be welcome.

Will you be having any heating on the 1^st floor? (e.g. Radiators).  My reason for asking is that it will impact your RHI payments (reduce them).  If nothing is going on the 1^st floor, do you want the ASHP sized to cater for the heat loss from the Ground Floor only?  If not, and you are relying upon heat migration to provide for the 1^st floor, you will need to put all of the heating for the whole house in via the ground floor.  This may make the Ground Floor too warm or the 1^st floor may not get adequate heat migration to heat it.  As you are also having an MVHR system, when it is cold outside, the incoming air will be lower temperature than the air leaving the house.  This will cause a noticeable cooling of the 1^st floor non-wet rooms and you may need supplementary heating.

 

[Jeremy Harris]

I'd say, from experience, that you certainly don't need heating, as such, on the upper floor, and only very modest heating in the slab.  The exception would be that it is nice to have some very gentle warmth in the bathroom floors, and the cheap and easy way to do that would be to fit some low power electric heating mats under those floors  to provide a tiny amount of comfort heating of the floor itself, nothing more.  Low power heated towel rails will need to be used in moderation, as they can easily over heat the bathrooms.

 

We fitted electrical outlets on the bedroom walls, so we could fit small panel heaters if needed - they aren't needed at all, so I'm glad we didn't go to the expense of fitting heaters.

 

UFH would be a massive over-kill for the first floor, and you only need a very tiny heat input to the ground floor slab.  We run our ground floor UFH with a flow temperature of around 24 to 25 deg C, and the heating only comes in for around an hour a day in pretty cold weather.  We have a stupidly big ASHP, a 7 kW model, for our 130m² house.  A 3 kW ASHP would have been plenty big enough, with lots of spare capacity, had one been available.  Our worst-case heating requirement, with no one in the house, and nothing in the house switched on and providing waste heat, our house needs around 1600 W of heat when it's -10 deg C outside.  In practice, we never need that much, as two adults chuck out around 200 W, plus there is always stuff on, like computers, TVs, cookers etc that put out a fair bit of heat.

Edited October 9, 2017 by JSHarris

[Heppy]

Thanks for your help.  We have been told there is a back up heating element to go into the MVHR to compensate for inadequate heat migration. Have you heard this before?

[PeterW]

Welcome !

 

MVHR can have backup heating but its not that efficient due to the low flow rates - its ok to take a chill off an incoming airflow but will not warm it to the necessary temperature unless its creating a lot of heat input. As @JSHarris said - and a number will agree - the best approach is to use localised heating where required in bathrooms and then let this supplement what will most likely be a low heat requirement.

[DH202020]

December will be our 1st year in our detached  3 bed MBC built house,  we went for the 180mm frame with additional 25mm Insulation.

Underfloor Heating ground floor only...in winter the upstairs is 1degree cooler,  no additional heating at all,  no towl rail heating... Nothing!

Towls dry overnight or in 4to 5 hours no probs.

our MVHR can warm the house  by 9degrees,  only needs 3hours of sunshine during the day and by morning (if  temperatures drop down to 10 degrees over night)  it's around  19-20 degree at 8 am.

our mvhr does not have any additional heating!

 

[Bitpipe]

We did more or less exactly what Jeremy proposed and we have a large 400m2 house over four floors (basement, 2 above ground, room in roof).

 

Passive MBC timber frame and basement.

 

No heating in basement, UFH on ground floor (which is timber suspended, not concrete), cheap electric mats under tiles in bathrooms and wet towel rads. Nothing in room in roof.

 

Basement temp never really changes - ground floor is comfortable and bedrooms are 2-3 degrees cooler (which we like). 

 

My plan B was to tap into the towel rad circuit and put a small rad in each bedroom, but this has not been necessary.

 

Your main problem will be overheating in summer - plan for that instead (external window blinds etc..).

 

[Jeremy Harris]

As @PeterW says, MVHR is pretty weak at providing heat, even with a post heater.  Our Genvex can, in theory, provide around 1.5 kW of heating.  In reality, because MVHR only moves a small amount of air (one house air change every 2 and half hours or so) the ability of heated MVHR to distribute heat is fairly limited.  OK for just maintaining a little bit of heat, but not a great deal of use for warming the house up from cold.

[ragg987]

We have ufh ground and basement. Direct electric towel rads in first floor bathrooms. MVHR upstairs has 4 supply ducts (4 bedrooms) and we have 1kW electric heater feeding those with a thermostatic timer on the landing.

MBC timber frame.

 

Our experience last winter (our first in the house) was upstairs was 3 to 4 degrees cooler than downstairs, too chilly for us really, so I used the MVHR heater for a couple of hours early evening to max out at 20C. (We like it quite warm). Also used the towel rads at lowest setting to keep bathroom warmer.

 

We would not be comfortable without heat upstairs.

 

Our MVHR heater is a 1kW unit, I think lower might have been better for the 4 outlets, if airflow is too low then the safety switch on the heater trips.

 

I would say your advice from ESP matches our findings.

 

One option might be to use your ASHP to earn the MVHR air to upstairs using a water heating coil. This will complicate your plumbing and control, but might protect the RHI?

 

FYI I did not bother with RHI as the premium of an approved installation was around £4k.

[ragg987]

Just to clarify, our MVHR heater only serves upstairs, we did this by having a separate manifold which has an electrical heater in line.

[Jeremy Harris]

9 minutes ago, ragg987 said:

FYI I did not bother with RHI as the premium of an approved installation was around £4k.

 

 

We didn't bother with RHI, either, it was completely pointless and would have cost us far more than we would ever have got back via the payments.  For us the payments would have been around £80 a year for 7 years, the additional cost of using an accredited supplier/installer/product so we could claim the  RHI would have added way over £2k to the installation cost. So, we would have been paying out over £2k up front in order to save less than £600 over 7 years.  We would have been nuts to even think about the RHI. 

 

FWIW, I'm convinced that RHI is only really aimed at older houses, with a relatively high heating requirement, not new houses than will inevitably need a lot less heating.

Edited October 9, 2017 by JSHarris

[jack]

Welcome to Buildhub.

 

2 hours ago, Heppy said:

If not, and you are relying upon heat migration to provide for the 1^st floor, you will need to put all of the heating for the whole house in via the ground floor.  This may make the Ground Floor too warm or the 1^st floor may not get adequate heat migration to heat it. 

 

This assumes you need high flow temps to keep the house warm in winter. As Jeremy said above, that isn't necessary in a house with this level of insulation and airtightness. We run at 25^oC, which is the lowest temp I can get out of our ASHP in heating mode. That does us fine during even the coldest spells in winter (as an experiment, I did try a temperature compensation curve that edged the heat up to around 28^oC during really cold weather, but we roasted!).

 

We still haven't switched on our heating yet despite having concrete floors throughout the ground floor of our house. It's starting to get a bit cool, but my wife hasn't started complaining about the cold yet, so it can't be all that bad!

 

2 hours ago, Heppy said:

My reason for asking is that it will impact your RHI payments (reduce them).  If nothing is going on the 1^st floor, do you want the ASHP sized to cater for the heat loss from the Ground Floor only?  

 

I can't see why the RHI would be affected by not having upstairs heating. From memory, you calculate the whole house heat loss and figure out how much energy is needed to heat it. Why would having heating upstairs change your heating requirements? (edited to add: perhaps they're assuming you'll need higher temps downstairs to cope, which brings about a penalty per the RHI - not sure).

 

I also don't understand the comment about sizing the ASHP to cater for heat loss from the ground floor only. Surely you size it for the heat loss of the house, in which case it doesn't matter how it's split between upstairs and downstairs.

 

That said, I'm another with an MBC house. Unfortunately, we installed no heating upstairs. It's usually 1-2 degrees cooler in the bedrooms, which is fine, but I'd firmly recommend some form of low level heating to take the chill off the bathroom floors. UFH heating would be ideal. Electric may be useful to avoid getting too much heat into the structure, but if it's only on for a short period morning and night at low temp, I think a wet UFH system would be fine too. You do need space for it - annoyingly, we had MBC drop the joists an extra 50mm to allow space for UFH build-up in the bathrooms upstairs, then changed our minds and built it back up!

 

2 hours ago, Heppy said:

We have been told there is a back up heating element to go into the MVHR to compensate for inadequate heat migration. Have you heard this before?

 

It won't be enough to heat the house all year round, but it may be useful to take the edge off the slightly cooler incoming air from the MVHR. It's not really a primary form of heating, but more a way of making things more comfortable by making up for the MVHR losses.

 

As someone said above, think hard now about how you're going to manage potential overheating. We decided not to include external blinds on one large east facing window, and we get a huge amount of solar gain through that in the morning during summer. The external blinds on the western window do a sterling job of keeping the heat out though.

 

1 hour ago, JSHarris said:

FWIW, I'm convinced that RHI is only really aimed at older houses, with a relatively high heating requirement, not new houses than will inevitably need a lot less heating.

 

Agree with that. An interesting point, though, is that there are several accepted ways of calculating heat loss for the RHI (this is from memory, so don't quote me!) I don't doubt that there are ways to manipulate the calculations to end up with an energy consumption estimate that's far more than the house would actually use. Still not sure it would be enough to make the RHI worthwhile in most cases, unless you can find a tame RHI installer who's willing to certify someone else's work. 

 

[le-cerveau]

8 hours ago, Heppy said:

Will you be having any heating on the 1^st floor? (e.g. Radiators).  My reason for asking is that it will impact your RHI payments (reduce them).  If nothing is going on the 1^st floor, do you want the ASHP sized to cater for the heat loss from the Ground Floor only?  If not, and you are relying upon heat migration to provide for the 1^st floor, you will need to put all of the heating for the whole house in via the ground floor.  This may make the Ground Floor too warm or the 1^st floor may not get adequate heat migration to heat it.  As you are also having an MVHR system, when it is cold outside, the incoming air will be lower temperature than the air leaving the house.  This will cause a noticeable cooling of the 1^st floor non-wet rooms and you may need supplementary heating.

Have to say this sounds like salesman bull**it, knows nothing about your house and is just quoting from a standard formula from his playbook.  As the others have said modern passiv type houses don't follow the norms, work it out for yourself and tell them what you require, not what they want to sell!

[Bitpipe]

Just to add, we bought one of those fancy Dyson hot/cold fans for our time in the caravan (hasten to say we wrangled a staff discount from a friend, extortionate otherwise) and it's been used now and again in the attic rooms when we have a guest staying over.

 

With a highly insulated airtight house, any heat you inject tends to hang around - the only challenge is getting it where you need it. Convection works very slowly with low temp UFH which is why our upper floors remain a few degrees cooler.

 

Again, make sure you have a plan for managing overheating - this will be your main issue. By luck we had designed large electric Velux at the top of our stairs / atrium that are pretty effective stack ventilators at night but we still need to do more to control solar gain in the evening.

[Heppy]

Thanks everyone. Has anyone got any experience of Earth Save Products please 

[Jeremy Harris]

38 minutes ago, Heppy said:

Thanks everyone. Has anyone got any experience of Earth Save Products please 

 

My experience was that they were a very helpful company.  I spent a long time talking to them and asking them all sorts of questions, and they responded well.  I didn't use them for a few reasons.  Firstly, it was pretty clear that they were importing Chinese units, adapting/modifying or even reassembling them and making sure they had proper (rather than fake) CE approval.  Nothing intrinsically wrong with this at all, but they weren't 100% transparent about it and only admitted this was what they were doing when presented with evidence of dozens of identical looking bits of kit on the Alibaba Chinese marketing web site.

 

Their prices were pretty reasonable, but the technology, especially inside the heat pumps, was a bit older than that in common use by the big name brands, like Carrier, Panasonic, Mitsubishi, etc.  In particular, when I was talking to them they didn't seem to offer any inverter controlled machines, although that may well have changed now.

 

As others have pointed out, low energy homes aren't really their forte.  They have installed systems that work OK in one or two, but they didn't seem to have an in-depth understanding of the very low heating requirements needed, and this then had knock on effects with the hot water systems they offered, as in the main their hot water systems are designed to draw excess heat from the house to heat the hot water, and in winter, in a low energy home, there won't be any excess heat.  This means the heating system for the house has to be increased in capacity in order to be able to supply the additional house heating needed just to then feed heat from the house air to the hot water system.  Not a particular problem, and it can be made to work, but it is a fair way from being an optimal solution, IMHO.

 

Finally, there was one thing  a year or so ago that really seriously annoyed me about them.  They were marketing a Chinese made MVHR with integral air to air heat pump, very similar to the much more expensive Genvex.  They were using the name Genvex in their advertising, and in the original user manual they had, or more likely the original Chinese manufacturer had, just lifted some images directly from the Genvex installation manual, showing a Genvex Premium 1 unit, and labelled as being their own machine.  This was copyright abuse, in my view, and should not have been allowed to happen.  Admittedly it was only on their Ebay outlet, I believe, and I'm far from sure that ESP realised that the images had been just copied from the Genvex manual, or that the unit itself was literally a "Chinese copy" of a Genvex, but even so it made me wonder a bit.

 

Having said that, in all the dealings I had with them they seemed honest and generally trustworthy.  If you are looking for a budget supplier, then they are probably around the cheapest going.  My only concern would be over long term support, given that a lot of their products are Chinese imports, in one form or another.  Nothing wrong with that in principle, many of the components in some of the big brands will be Chinese, and none the worse for that, it's really a question of whether ESP will have the resources to supply service parts and spares in ten years time.  Maybe they will, they've been around for a few years now, so there's no obvious reason to suggest they are likely to be unable to supply spares in the future.

 

 

Edited October 10, 2017 by JSHarris

[Heppy]

My thoughts exactly. We have been back and forth trying to negotiate what we want and what they think we have should have. We have gone from underfloor heating up and down to just downstairs and a ASHP Varimax 20 down to a 12 Varimax. This is our first build and only on doing some research are we coming to our own conclusions, which we hope are right. And having forums like this to chat to other people who have enormous amounts of knowledge.

[TerryE]

@Heppy Have a look at Jeremy's calculator and blogs such as his and mine where we go through some of the calculations.  If you've got an MBC frame and warm slab, and decent Passive-class Windows, airtightness and MVHR then you'll only need to sustain maybe a 1Kw into the slab at peak during Dec/Jan.   Putting enough heat into the house isn't the issue, as others have said: you will need to pay more attention to how you keep it cool in spring through autumn, plus how you trickle heat the UFH to stop roller-coaster overruns. 

[ragg987]

I can recommend https://www.theunderfloorsuperstore.com/ , they really took this in their stride despite not having much experience with PH-level houses and helped me to get a good system together at a great price. My own plumber and electrician did most of the installation apart from UFH which I put into the screed package. We have a 7kW HP serving 330m2 house so sounds like your sizing is quite large at 12kW.

 

I also spoke to a number of suppliers including ESP, but in the end I did not feel their Ecocent HP that extracted heat from the house was right for us.

[Jeremy Harris]

1 hour ago, ragg987 said:

I also spoke to a number of suppliers including ESP, but in the end I did not feel their Ecocent HP that extracted heat from the house was right for us.

 

That was exactly the conclusion I reached, after a lot of time spent thinking about it.  I was really committed to using the Ecocent, and had some very useful discussions on the GBF about it, as well as with the helpful ESP guy on the stand at the Swindon show, but in the end the sums just didn't make any sense at all. 

 

I had a house that needed a few hundred watts at most to keep it warm, yet when we needed hot water I'd have had to increase the heating to the house to over 2 kW, just to provide the heat that could be pumped from the house into the hot water.  There's no doubt this can be made to work, but it seemed a bit daft to me to massively increase the heating input to the house, just to suck that heat out again immediately and use it to heat the hot water.

 

In the end, I came around to the view that the heating system and hot water systems needed to be treated separately, as the requirements were so wildly different.  I had a heating system that only needed to deliver a few hundred watts to the whole house in winter, but needed a hot water system that could deliver a lot more.  As we don't have gas available (if we had I'd have just fitted a gas combi - far and away the best solution for our hot water needs) I opted for a separate thermal battery heat store, that's electrically heated using either excess power from solar panels or can use off peak electricity.  The latter is close to the running cost of a heat pump, in terms of energy cost.

 

Edited to add:

 

I found the thread I started on the GBF back in 2012 about the Ecocent and a more recent one.  It's interesting reading, although back then it was early days as far as estimating our heating requirement, and I had over-estimated it by a fair bit, it seems.  In reality it's perhaps half the figure I'd estimated back then:  http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8326

 

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13490

Edited October 10, 2017 by JSHarris
Added link to another discussion

[Declan52]

I would tend to agree with all what has been said here already. There are quite a few MBC builds on here and I would pay more heed to real life experiences than what a salesman is trying to pitch. 

Put your sums in the calculator and see what it gives you. 

[dogman]

Interesting as i am currently talking to them as well. Spent a good hour today at their office chatting to Nick and he fully understands the concept of a passive MBC timber frame and heating the groundfloor only. In fact he has responded to the need for a low temp blender valve and can now supply this:-

 

I am taking a slightly different view on upstairs and just picked up 3 fan coil rads from them as i want to be able to cool the upstairs in the summer.

 

 

[dpmiller]

there's a high-spec inverter ASHP imminent too.

[dogman]

@dpmiller you mean the Heliotherm. Saw one today. A bit outside my price range

[dpmiller]

@dogmanDon't think so. They alluded to something with a more standard format, coming at the end of the month?

Edited October 10, 2017 by dpmiller

[dogman]

I was going for their Varimax H4-12, will ask next time i am in there as i need some more bits in a week or two before i get the ASHP