Heating and cooling: Heat loss calculations

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- CommentAuthorcascina
- CommentTimeApr 25th 2016
I am trying to put together a plan for a heating system on a new project. We are based in italy and the house is of concrete construction. I installed heating systems commercially in the uk for a number of years and did heat loss calculations on most of my installs to make sure the right boiler was selected for the job. To do this, I used the 'whole house heat loss method' using software from www.idhee.org.uk. Using this I had options to enter the dimensions of the property, current insulation, glazing, aspect, location etc. to come up with a heat loss figure which I would then use to size the boilers central heating load and de-rate the boiler as required.

I am now looking at a concrete house which appears to have no insulation in it. It is over four floors including the basement and the roof has 3 rooms and a bathroom within it under the pitched roof. Looking at the openings for the velux windows, the roof appears to be approximately 10" thick and is described by the builder and agent as 'cemento armature' which I think is reinforced concrete. What we want to do initially is to add EWI to the external structure, but the large roof was recently replaced due to a leak, with new battens and the original coppi tiles. This means within the roof space mostly pitched, we will be using IWI. Given all the surfaces are pitched concrete, I presume that this would be done in the same way as external wall, using an adhesive and then insulation screws/bolts drilled into the roof?

I will be doing the IWI straight away before winter, but the EWI may have to wait until next spring due to the rest of the work required from the builder. The question then is: how do I go about calculating heat loss before and after improvements?

Currently there is a 30 year old oil boiler and dead oil tank, so we are starting fresh. I am looking to install a wood burning boiler and have significant storage available in the adjacent barns for the wood storage. I would then be looking at having a pellet boiler to act as a reserve for when I am not there and my wife is unable due to childcare etc. I also like the redundancy of multiple input systems for when one breaks down in the depths of winter and I am away.

I have installed a few thermal stores before but normally to act as a buffer between wood burning stove with back boilers and gas boilers in SE England, but not to enable batch burning from log boilers. I would like the ability to batch burn as infrequently as possibly, so having calulated the heat loss, would want to size a thermal store appropriately to the log boiler, but oversize the log boiler for the house's heat loss to enable less frequent burning and also utilise the larger logs that appear compatible with larger log boilers.

We would also be looking to add thermal solar (I have a 30 tube ET setup in storage from a previous project) which should be able to provide most of our house DHW during the non-heating season. The main house is approximately 550m2 not including the basement.

Any help in formulating a plan would be most gratefully received as reading this forum has given me a massive appetite for getting this right first time round.

Thanks in advance.
- CommentAuthorSteamyTea
- CommentTimeApr 25th 2016
Do you have any idea what it currently uses energy wise?

You can work out the U-Values for the concrete walls once you find a suitable thermal conductivity value for the mix used. Google will help you out, but make sure you use SI units and not Imperial ones (the R-Value trap).

Also what is the airtightness like and the amount of solar gain? those two can greatly affect your calculations.
- CommentAuthordjh
- CommentTimeApr 26th 2016
Posted By: cascinaCurrently there is a 30 year old oil boiler and dead oil tank, so we are starting fresh.

How dead is it? I ask because it sounds like you won't have your insulation finished before this winter so you'll have a large heat load this winter, which will hopefully be a lot less in subsequent years. Which means you won't want to fit your shiny new heating system this year unless you have a plan to supply a lot of extra heat somehow. So it might well be better to resurrect the existing heater for this winter and start installing the new system next year, I think.
- CommentAuthorPeter_in_Hungary
- CommentTimeApr 26th 2016
Posted By: cascinaI would like the ability to batch burn as infrequently as possibly, so having calulated the heat loss, would want to size a thermal store appropriately to the log boiler

The typical ratio for boiler to TS is 1:50 so a 40kW boiler gets a 2000 ltr TS but you can go bigger, say 1:75. My system is 40kW with 2000 lts TS and I find that without much load on the TS one fill of the boiler will raise the temp. of the TS from 40 top to bottom to about 85 - 90 top to bottom. When the weather is cold then I have to refill the boiler part way through a burn. I am happy with the boiler / TS ratio I have (1:50) - which is just as well as ceiling and footprint would prevent a bigger TS

It is important to get your system properly set up to maintain stratification as this maximises the use of the heat available in the TS. What I did with my TS is detailed here

http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=13082&page=1#Item_8

And I am still very pleased with the results!

The general advice is to have a separate tank for DHW rather than a coil in the TS or a plate heat xchanger outside (which can really mess up stratification due to the high flow rates).
- CommentAuthorPeter_in_Hungary
- CommentTimeApr 26th 2016
Posted By: cascinawe will be using IWI. Given all the surfaces are pitched concrete, I presume that this would be done in the same way as external wall, using an adhesive and then insulation screws/bolts drilled into the roof?

I don't think that the mechanical fixings will be needed internally. They are used externally as belt and braces to help in the event of wind suction. Some of the manufacturers recommend that mechanical fixing are NOT used on certain types of insulating blocks as the blocks are so soft the screws have no holding power any way!
- CommentAuthorDarylP
- CommentTimeApr 26th 2016
cascina, depending on the inner face of your IWI product, try low-ex foam adhesive in a gun? Fine control and you can be as creative as you like with the adhesive ribbons...
- CommentAuthorGotanewlife
- CommentTimeApr 26th 2016 edited
I assume the underside of your ceiling is flat (ie no beams protruding)? Is the finish to the underside friable - ie old flaky, dusty cement? Insulated hammer in fixings (ie plastic mushroom heads with metal or plastic 'nails') will be really easy for you; I, and others on here, hammer them into the plasterboard where is crushes the plasterboard enough so that it doesn't sit above the surface or if it does it is tiny and can easily be covered when you tape and joint. (assumes you use pre-insulated PB - slightly more expensive but much quicker/easier to install).

What are you going to do about services? Services obviously include the electric cables for the light fittings but what about MVHR - you will need 125mm pipes to all the rooms within the roof area unless store rooms, and the extract in the bathroom should really be in the ceiling or as high as possible and preferably over the shower or the farthest point from the door.

This is a good example of trying to cover too many unrelated areas on one post - you could easily have a jolly good discussion on the IWI of under your roof and not cover anything else and for sure not address the topic title.

Talking of which - you really should do as ST says - grab any of the quick and easy tools out there and give yourself a starting point - then just make a blind stab at what your EWI and IWI will be, for all glazing use a Uw of say 1.5 and do it again. Hey presto an idea of your heating load. Your airtightness will be excellent and, to the envy of almost all on GBF, will take little effort or skill given you have rendered solid walls and will have new windows and doors.

One big thing we might have overlooked - do you have wrap around balconies? - 6 x French doors suggests as much - boy do balconies screw up EWI!!!
- CommentAuthorcascina
- CommentTimeApr 26th 2016
Thanks for the responses.

Steamytea,

It is impossible to know the current usage as the house has been vacant for over 10 years and connects to another house which was part heated from the same system, where the carers/farm manager lived. I presume from what Gotanewlife is saying that airtightness will be easier to manage. The only thing that will require some closer thought is the whole footprint basement. All the doors are ventilated and metal including the external doors which open up into an intercapedine (about 1 metre wide and with metal grilles to ground level. While some of this is the boiler room, we would like to use some of it as a games room, so will have to put some thought into where the insulated envelope of the house ends.

With the u-values from the net, would you then go about examining floor by floor the heat losses or is there still a way of calculating the whole heat loss of the house.

djh,

The heating system has been dead for over 10 years since the previous owners died- nothing happens fast here. The oil tank is heavily corroded and in a very poor state so I don't think it could be reinstated without considerable cost.

Peterinhungary,

Thanks for the numbers. I will peruse your thread. If you have a 40kw boiler, what is the heat loss of your home. I had it in mind, that if the heat loss was, say 25 kW, that you could install a larger boiler as you have to capture more heat from a single burn into a thermal store to enable less frequent charging and the boiler will not be running continuously, but others seem to be suggesting that it should be sized smaller and closer to the heat loss of the house if I am not misreading.

How does your boiler prioritise the DHW heating before the TS? Are there thermal diverter valves? I will have a read of your thread as it is probably covered there.

Darylp,

I have used Kingspan kooltherm in the past with dot and dab and then mechanical fixings, but will look at low-ex foam adhesive too.

Gotanewlife,

The ceiling surface is smooth with a well sealed non crumbly finish. Only part where I can see it being fun is the apex, where the render/plaster has been smoothed over to create an arc connecting one pitch to another with a neat angular join. I imagine this will be slighter trickier to detail and involve some foam.

As for utilities, the whole roof space is habitable excepting the void behind a dwarf wall which is about a metre high and runs around the perimeter and has a small hatch to get access where you could easily crawl around. This should allow access to all services. Does the MVHR only need to serve the loft space or will it be required for the bedrooms and bathrooms on the first floor. I must say, that is a whole field I haven't looked too closely into. I came across it in a lot of housing association installs and the vents were normally blocked with socks because they found it noisy! The architect across the hall told me not to finish the windows and doors in too airtight a manner to avoid ventilation and mould issues. When I mentioned MVHR he looked blankly at me and gave a shrug, telling me to make sure I didn't fill all the gaps!

You are indeed correct. There is a large wrap around balcony on the first floor to 3 bedrooms and then another portico covered terrace onto which 2 open. I presume the cold bridging is the issue here? Are there any neat solutions or is it something that we have to accept?
- CommentAuthorGotanewlife
- CommentTimeApr 27th 2016 edited
Posted By: cascinaWith the u-values from the net, would you then go about examining floor by floor the heat losses or is there still a way of calculating the whole heat loss of the house.
The one I used just had whole wall dimensions. With your massive, massive non-fixable cold bridges of balconies and roof/wall join (ie EWI will not meet IWI at the roof) any clacs you do will be seriously approximate.

Seriously now - what ever you do do not listen to your architect or probably any geometra locally - they are so far in the dark ages it scary. You need someone who will do it your way, who wants to improve and learn and who will not lose face if they find they don't know something. BTW - since you have your habitability certificate (you do don't you) - the only thing you need sign off for is the EWI. Unless you need to re-assign correct uses to your rooms that is and want to do it legally.

I presume you have some soon to be demolished open fires to keep your family warm in one room at least for the winter - you were not under the impression you would get this done over the summer I hope....
Ref roof space - I took all my dwarf walls down and in one place recovered good space and in another put it back up taller and gained a really good storage space. If you take them all down then you can IWI all over and then re-instate them exactly where you want them using long frame fixings to attach the PB sud wall ceiling U profiles or metal plasterboard fixings - depending. Otherwise yet more cold bridges where stud wall meets ceiling AND you still have to IWI in the void (or 'EWI' the stud wall and put loft insulation on the floor of the void. Bite the bullet - take them down!

You should plan on MVHR for every normally inhabited room in your house - however, you can have more than one MVHR system and or individual ventilation solutions for single rooms. There are shallow but wide 'pipes' (60mm deep) which I suggest you look into putting in your bathroom under the roof, via a suspended (or big battened) ceiling. MVHR is really quiet! Well unless it is badly specified and badly installed anyway.

Very quickly either go for Wood Burner or go for pellet burner. Each have different requirements. I have 40kW with 2500 ltr TS (no space for bigger but wish it was bigger) I heat my 450m2 house throughout to 21 deg at a cost of up to 1000 Euro pa. Suggest tank-in-tank TS solution with solar to top coil and wood burner to bottom coil. I have 5 avg Flat plates and get 99% coverage of my DHW during the 6 months (ish) of year when I don't need space heating but I have to cover 2 up for summer. Wood cost less than pellets but sounds like you need to go the pellet route since you appear not to be at home reliably.
- CommentAuthorGotanewlife
- CommentTimeApr 27th 2016 edited
Oooops - of course you can also IWI the inside face of the dwarf walls and loft insulate the void behind - that moves the cold bridge somewhere acceptable (ie down stairs ceiling ) and keeps the current dwarf walls.

Also, you can fit a flat section across the apex allowing either on 125mm pipe or 2 204x60 'pipe' along for MVHR - either insulate the pipe and IWI under or (much better) IWI above and PB below - (when you get to the detail stage then you will want to understand choices of vent fitting, esp whether level with ceiling or extended a little as a compromise). Easier than try to shape IWI to the funny curve as well!

Generally, I get max 2 weeks below -5, snow once a year for max week, and +35 for up to a month. What about you. What was your max internal air temp last summer? - big diff from middle to top floor?
- CommentAuthorPeter_in_Hungary
- CommentTimeApr 27th 2016
Posted By: cascinaPeterinhungary,

Thanks for the numbers. I will peruse your thread. If you have a 40kw boiler, what is the heat loss of your home. I had it in mind, that if the heat loss was, say 25 kW, that you could install a larger boiler as you have to capture more heat from a single burn into a thermal store to enable less frequent charging and the boiler will not be running continuously, but others seem to be suggesting that it should be sized smaller and closer to the heat loss of the house if I am not misreading.

How does your boiler prioritise the DHW heating before the TS? Are there thermal diverter valves? I will have a read of your thread as it is probably covered there.

I have no idea what the heat loss of the home is. The gasification boiler was installed 22 years ago without a TS and needed help (wood burning stoves) when it was cold (2 houses, no DHW) Now after some new windows, EWI and other insulation and a TS it copes well and supplies DHW (2 houses) in addition without the need for additional help. DHW is supplied by a separate tank run as a load on the TS. The boilers only job is to heat the TS. Boiler use in winter is about 1 -1.5 loads / day and summer (DHW) is about 2/3 load twice a week depending on guests etc.
- CommentAuthorSteamyTea
- CommentTimeApr 27th 2016
What is the mass of a 'load'
- CommentAuthorGotanewlife
- CommentTimeApr 27th 2016
about a wheelbarrow full!
- CommentAuthorcascina
- CommentTimeApr 27th 2016 edited
Gotanewlife

Thanks for the comprehensive reply. The house is currently officially 2 dwellings of 16 and 10 rooms respectively. The other houses have had their use changed to C2? from memory which has the effect of significantly reducing the rendita catastale (I think that was the impact).

It currently has 3 open fires, which I am getting abuse for not wanting to leave from every Italian who sees it. We will be removing one as it is what will become our master bedroom and replacing the largest in the living room with a wood burning stove. I think you may be right that a pellet boiler is the best option given the additional hassle of me not being around with work. I do love redundancy in a system.

I completely get what you say about the dwarf walls. I hadn't realised the impact of the cold bridging detail. Our builder suggested 25mm but when i smiled and told him he'd have to humour me with 100mm plus, he patted me on the back while laughing and said he'd fit whatever I wanted. I think he thinks my plans for insulation are a bit peculiar but is happy to work with it. The idea for the MVHR is great running in the apex. That as a subject alone is something I need to get my head into and study having had no exposure to it at all.

We have cold winters at below zero for a month or two, but snow for only a couple or few weeks. It was where my wife grew up but we are currently living an hour away on the coast. All parties (an inherited property with disagreement between the parties, so it's taken months) have signed the offerta and registered the contract. We are just waiting on the valuation for the bank which is being held up by the repartitioning of the vineyards from the house. I'm trying to get ahead of the game with planning building works. The geometra for the lands is the agent's brother and is pushing things along fast. We have the atto provisionally set for the end of July and our builder has had a quiet couple of months so is keen to start work at the beginning of August because of this.

Who makes your tank in tank TS? Why would you go bigger if possible? There is an old DHW cylinder which is in a poor way with corrosion and leaks and needs replacing, but has a flow and return for solar which they had in the 70s/80s up into the void space behind the dwarf walls in the loft. It is in the front of the house (southern perspective) whereas the caldaia is at the rear (with steps down from the rear of the property) meaning potentially long runs for the flow and return from the solar panels.

Peter_in_Hungary

Thanks for the info. I guess a lot of it is approximations and then as you move forward, tweaks to try and optimise the system.

So much to take in.

Did I mention that we want to be in there for Xmas? We've only got 23 coming over this year....

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