How long to heat up a heavy house

[AliG]

Hi,

 

We have had the heating running for around 7 days and the interior temperature of the house was around 11 degrees today according to the builder, the outside temperature has collapsed to 3 today.

 

This is clearly not helped by them being in and out all day leaving does open etc. Also the front door is not in so it is just a frame with waterproof sheeting over it.(It may be in now) the MVHR is not on etc.

 

I tried to calculate how much energy required to get the house up to temperature.

 

I reckon there is around 600tonnes of concrete and blockwork inside the heated envelope. This would require around 3000kwh of heating to raise the temperature 20 degrees. Plus any heat losses which are probably running at a few hundred kwh per day in the current unfinished state. Heating up the air will require a negligible amount of energy in comparison. 

 

Does anyone have any experience of heating up a blockwork or ICF house and how long it took to get up to temperature. We need it to be in the high teens by Tuesday for the kitchen to go in. I had not really considered this but due to the much higher weight of this kind of construction, even if it is as well insulated as a wooden house it will require much more energy for initial heat up. The heating went off at one point after running through 2 large bottles of Calor gas in a 4 days. That seems to be around 1300 kwh of gas

 

We are restricted on how much we can turn up the heating flow temperature so as to not cause cracking. I thought this was not a problem as the flow temperature should not have to be high. This is true once the house is up to heat but starting from a low temperature I am worried that the 30-35C flow I think we are running will not be enough to heat the house up quickly.

 

 

 

[ProDave]

Not directly related, but our previous house, a timber framed house with UFH on both floors. When we fired up the heating on that, in November, it took about 4 days to get up to temperature.  Initially I doubted the heating was adequate as the first day didn't seem to do much apart from burn a lot of oil.  But once warmed up that proved to be a reasonably economical and certainly very warm and comfortable house.

 

2 bottles of gas in 4 days sounds like a lot.

 

 

[jamiehamy]

It's an interesting question. I'm tracking this just now as we're starting to get out house up to temperature. I'm doing it room by room really, keeping doors closed. In the kitchen I started 3 days ago at 13degrees air and 12degrees slab (no ufh). Running a 1400w radiator constantly has air at 20degrees and slab at 17.6 on surface. I've just started our bedroom on same. 24hour later slab is 2 degrees warmer. For nothing I imagine there's still a lot more heat to be absorbed but it will probably take a good couple of weeks. 

 

Do you have a handheld Ir heat sensor? Handy things to measure surface temperature. 

 

I'm afraid it's not very scientific, must maybe doing individual rooms could be quicker than whole house for the time being? 

[AliG]

I do have an IR camera, I might take it round on Sunday, the floor definitely felt warmer to the touch.

 

Looking at the gas use, it might be that I would need around 6 bottles over a week and a half to get it up to temperature as I reckon around 5000kwh including losses.

 

I don't know how much heat the builders have been letting out and the massive drop in outside temperature in the last couple of weeks won't have helped.

 

The builder has suggested doing a room at a time, but we don't have the heating controls connected up yet, so we are just running it with open manifolds.

Edited December 8, 2017 by AliG

[oldkettle]

Is running a few electric heaters an option? At least they could help you get the temperature in the kitchen up. It will probably heat air only though. What exactly is required for installation, air or wall temperature? 

[TerryE]

1 hour ago, AliG said:

I reckon there is around 600tonnes of concrete and blockwork inside the heated envelope. This would require around 3000kwh of heating to raise the temperature 20 degrees.

 

Ouch!! If you look at my last blog post you will see my calcs:

And I reckon we have 33 tonnes of concrete / wood/ plasterboard within our envelope.  600 tonnes seems a huge amount.  At the moment we aren't living in the new build so we don't have indirect waste heat in the house's heating mix, but my rough estimate is that 7hrs @ 3kW (my E7 quota) is keeping the temperature level but I am slowly cranking the base tenp up with another 2 hrs.  We are now at a toasty heat level. after about 10 days of heating.  All for < £2 / day.  

[Nickfromwales]

It's getting heated from scratch for the first time, you dont have a front door, you don't have the mvhr running, and the doors which are there are like saloon doors ?  Your going to chew through a lot of gas, not exactly a game changer ?

Turning up the flow temp by 2-3oC should make a big difference so give that a whirl first and see what difference that makes over 24 hrs. 

To reinforce this I'd get some paraffin space heaters in on hire and blast some hot air through at the same time to get things moving. If you have deadlines then don't hang about, get the place warmed through by whatever means necessary. If there is a little cracking of joins in the plaster etc then so be it, it'll happen anyhoo to some degree so just bite the bullet and get the process shoved along a bit, even if it is against its will and a bit expensive on fuel. It's not going to happen any other way tbh.  

[Ian]

@AliG

part of your problem is likely to be that the building is still drying out. Unless the walls and slab were completed over a year ago 600 tonnes of concrete means that there will be a hell of a lot of excess water that still needs to evaporate from the structure of your building.

I agree with @Nickfromwales that you need to crank the heat up although I personally wouldn't recommend paraffin heaters as they release approx 1 litre of moisture vapour for every 1 litre of fuel burned. With a building like yours is at the moment you could create a bad problem with condensation.

Edited December 9, 2017 by Ian

[PeterW]

A mix of industrial dehumidifiers and heaters may be what you need here to keep moisture levels low and heat high. 

 

If the front door is only sheeted, consider getting a couple of sheets of 100mm insulation from the merchants and make a solid insulation “plug” with it as that will help retain heat 

[TerryE]

5 hours ago, Ian said:

part of your problem is likely to be that the building is still drying out. Unless the walls and slab were completed over a year ago 600 tonnes of concrete means that there will be a hell of a lot of excess water that still needs to evaporate from the structure of your building.

 

When was the concrete poured?  We only have 10cm across most of our slab and it still took 10 months to dry out properly (Nov -> Aug). Before that if you laid a square of polythene on the dry slab for a week or so, then you'd see the colour change as the residual moisture came to the surface.

   

So, I was thinking also about this.  600 tonnes of concrete = maybe 100 tonnes of water to be evaporated off.  Let's guess 100 tonnes of water, this will take 2,200 × 1000 × 100 / 3600 = 61,000 kWh latent heat (loss) of evaporation.  Even if it was half that, this is still a lot of heat energy.  If the structure is damp, then cranking up the temperature will mean that more dampness will evaporate off and the internal RH will just stick near 100%.  So I'd concentrate on getting it properly dry before trying to warm it up too much.  As @PeterW says, a couple of industrial dehumidifiers running around the clock will condense out this water and return the latent heat back into the structure. 

[Ferdinand]

TAking figures which are the max. Much less may make adequate comfort, or close off half the house behind polythene drapes for now.

 

A stonking transportable industrial dehumidifier in ideal conditions (eg temperature of 35c) might pull out 100l a day.

 

If you have 100 tons of water to remove, that would take 1000 dehumidifier-days in theory.

 

Such a beast will cost about 750 a 1000 ukp to buy new, and well over £100 a week tor rent, ish.

 

IF you are serious then I can recommend the smaller Broughton CR40  models as compact for their performance. I bought one secondhand and it is a heavy duty but small 40l/d machine. That and a 60l/day machine dried out the plasterwork skim in the LBB in 2-3 days to a point acceptable to paint, running at a high 20s C temperature. THe LBB is 64 sqm, and all ceilings are 2.4m, 85% was skimmed.

 

New they are about 350-400 and you would need enough for a bulk discount, but there is the prospect of selling them on here.

 

It might make sense to buy 5-6 and 3-4 fan heaters (Screwfix?) and employ a man to sit there all day as security with windows and doors open. Then run dehumidifiers and heaters overnight.

 

If any of your guests have asthma they could be very uncomfortable above say 70% RH.

 

Best of luck.

 

Edited December 9, 2017 by Ferdinand

[Ian]

3 hours ago, TerryE said:

 

When was the concrete poured?  We only have 10cm across most of our slab and it still took 10 months to dry out properly (Nov -> Aug). Before that if you laid a square of polythene on the dry slab for a week or so, then you'd see the colour change as the residual moisture came to the surface.

   

So, I was thinking also about this.  600 tonnes of concrete = maybe 100 tonnes of water to be evaporated off.  Let's guess 100 tonnes of water, this will take 2,200 × 1000 × 100 / 3600 = 61,000 kWh latent heat (loss) of evaporation.  Even if it was half that, this is still a lot of heat energy.  If the structure is damp, then cranking up the temperature will mean that more dampness will evaporate off and the internal RH will just stick near 100%.  So I'd concentrate on getting it properly dry before trying to warm it up too much.  As @PeterW says, a couple of industrial dehumidifiers running around the clock will condense out this water and return the latent heat back into the structure. 

@TerryE @AliG

your external wall design will normally be such that they are vapour open to the outside but vapour closed internally which means it's only the plaster that will be drying to the inside of the house so the bulk of the heat you're putting in will be forcing the structure moisture outward. Humidity shouldn't be a massive issue but it will take a long time to heat the house up because of the latent heat issue

Edited December 9, 2017 by Ian

[TerryE]

@Ian, that will be true for external walls, but not for internal ones and any floor slabs, and as you say the latent heat loss will still be an issue.

[Nickfromwales]

8 hours ago, Ian said:

I personally wouldn't recommend paraffin heaters as they release approx 1 litre of moisture vapour for every 1 litre of fuel burned. With a building like yours is at the moment you could create a bad problem with condensation.

Every day is a school day . Never knew that !

Its bottled gas or red diesel heaters then, as I doubt there is any provision to be running all these massively electric-hungry devices. A couple of big dehumidifiers will use a lot of juice, even if via a 110v tranny. 

Maybe get the sparky to cut a couple of chunky supplies in at the CU for temp feeds ( e.g. Stick a 32a C-form socket on each cooker feed ). Or just make sure your running them off different ring mains if the generic electrics are operational? 

A few cheap 12" oscillating desk fans blowing across the slab should help move air around to help the dehumidifiers out a bit too. 

[Nickfromwales]

Also @AliG you need to call a site meeting. Expailn to every guy / gal on site the importance of keeping doors and windows closed and drive the point home. 

Assuming they will do it isn't good enough, plus they need to be doing it when your not around too.

[Onoff]

If your slab in a new build is still drying out and you carpet over it prematurely or worse still laminate of some sort doesn't that trap moisture? Or is it breathable enough?

[AliG]

I had figured out that the gas heaters were a bad idea, they were using them for a few days before we got the UFH running.

 

The wight within the insulated envelope includes 550 square meters of 200mm thick concrete planks. These have been in situ for over 6 months and were probably manufactured around 9 months ago so I am guessing they are pretty much dried out.

 

Then we have around 1000 sqare metres of 70mm screed. That has been down for around 4 months so it will have dried out to a good extent. It has been some time since I have seen a damp area when someone put something down on the ground

 

Then we have the Porotherm clay blockwork, most of the internal walls are made of this and there is the internal layer of the external cavity walls. However, this has insulated plasterboard on it so maybe I should exclude it from what we are heating up. This was built between 6 and 9 months ago and the mortar is only 1mm thick so hopefully it is pretty dry.

 

The main recent wet trade has been plaster skimming all the walls and ceilings. Some of these were just done in the last few days, indeed they have not done the hall yet. It is only a few mm thick and seems to dry out after around 2 weeks.

 

The humidity is running at around 40% with the heating on but the temperature not that high, I will see how it is tomorrow with the heating cranked up a bit. But maybe most of the drying out has occurred.

 

It is definitely something to think about when scheduling a build and a much bigger problem due to the low current temperatures.

 

I thought the front door would be in this week, but it wasn't when I just drove past.

 

We have sanded and sealed the screed and started to tile, the wooden floor underlay has a damp proof layer, but they do not want to lay it yet.

 

Hopefully the temperature will warm up with the humidity not going too high. I have suggested that as it warms up we open the veluxes in the top floor to create a chimney effect and draw the moisture out.

 

More new tomorrow after I meet the builder

[TerryE]

52 minutes ago, Nickfromwales said:

Also @AliG you need to call a site meeting. Explain to every guy / gal on site the importance of keeping doors and windows closed and drive the point home. 

 

Nick, there is a caveat here.  If the total residual evaporateable water is too great and @AliG prematurely starts to seal the house, to heat it and to lay coverings like carpets then he's going to beset by mould and damp problems.  

 

I've just picked up A's last cross post and the 40% RH is a baseline; if the house is sealed it will only climb from that.  A, if you do want to start sealing and heating the house then IMO industrial dehumidifiers are an essential precaution.  What does our resident scientist say, @JSHarris?

 

[pdf27]

39 minutes ago, Nickfromwales said:

Every day is a school day . Never knew that !

Its bottled gas or red diesel heaters then, as I doubt there is any provision to be running all these massively electric-hungry devices.

Doesn't help - you'll get about a litre of water for every litre of diesel burned too, and bottled gas is slightly worse for the same amount of heat delivered. Essentially all the oil and gas derivatives are made of a mixture of hydrogen and carbon (natural gas has 4 hydrogen molecules and 1 carbon, while diesel has about 32 hydrogen molecules and 15 carbon molecules). The heat is given off by combining the carbon and hydrogen atoms with oxygen from the air, forming carbon dioxide and water. Pretty much the only thing you can burn without a lot of water in the exhaust is coal and similar smokeless fuels.

 

The actual calculation is:

1. LPG gives about 46 MJ/kg (12.8 kWh/kg) - that's lower calorific value so assumes the water from the combustion process will stay as vapour.
2. That means 78kg of gas is needed per 1,000 kWh.
3. They're either C3H8 (propane) or C4H10 (butane) - 10% or 8% hydrogen by weight respectively. That means the 78kg of gas will contain about 7kg of hydrogen gas.
4. Water is H2O - so 2kg of hydrogen gives 18kg of water.
5. So 1,000 kWh will mean about 60kg of water being released into the house. Unless well ventilated, it will all end up condensing out on cold surfaces.

[Jeremy Harris]

Worth noting that most of the water in concrete never, ever comes out of it, it gets used in the complex chemical reactions that causes Portland cement to set.  The reactions are complex and poorly understood, even now, but a fair bit of water goes into the intermediary compound Ca(OH)₂, that eventually (after literally years of absorption of CO₂) becomes the somewhat harder CaCO₃.  This is one of the reasons that concrete continues to age harden over the first few decades after it has set.

 

It's important that concrete not be encouraged to "dry out" for several months after it has been laid, as it continues to harden by the initial curing reaction (the one that absorbs water as Ca(OH)₂ is formed) for several months, at least three months, often much longer if the temperature is low.  If partially cured concrete (less than around 3 months old) is forcibly dried out, then the initial cure will stop, and there will be deep regions that remain not fully cured.

 

Generally this deep moisture never presents a significant problem.  It will end up being incorporated into the final matrix as one of the intermediary compounds, and won't present a problem by coming to the surface unless it is forced to by some means.

[Ferdinand]

2 hours ago, Nickfromwales said:

Every day is a school day . Never knew that !

Its bottled gas or red diesel heaters then, as I doubt there is any provision to be running all these massively electric-hungry devices. A couple of big dehumidifiers will use a lot of juice, even if via a 110v tranny. 

Maybe get the sparky to cut a couple of chunky supplies in at the CU for temp feeds ( e.g. Stick a 32a C-form socket on each cooker feed ). Or just make sure your running them off different ring mains if the generic electrics are operational? 

A few cheap 12" oscillating desk fans blowing across the slab should help move air around to help the dehumidifiers out a bit too. 

 

The 40l per day (at 35C 100% rh) commercial dehumidifier I mentioned says it uses 1.3A at 220/240v or approx 350W. Surprisingly low.

 

Your fan heaters to get it warm will be the main issue. Good job it s well insulated :-).

Edited December 9, 2017 by Ferdinand

[Declan52]

We moved into our block house 3 years ago at the end of sept and it took near 2 weeks to get the house up to a nice 21 degrees inside. Until you sort out the heat loss from the front door your going to struggle to get it anywhere near where you would like it. 

Can you board it over with insulation sheets and use another door for your main route into the house??

[AliG]

The front door is on site, I will try and make sure they put it in on Monday. I thought it was going in this week. Clearly it is going to be a big source of heat loss until then.

[TerryE]

6 hours ago, Ferdinand said:

The 40l per day (at 35C 100% rh) commercial dehumidifier I mentioned says it uses 1.3A at 220/240v or approx 350W. Surprisingly low.

 

40l = 40 × 2200 kJ = 24 kWh latent heat released for 8.4 kWh electricity so a CoP of ~ 4:1 --  pretty good, eh?

[Ferdinand]

58 minutes ago, TerryE said:

 

40l = 40 × 2200 kJ = 24 kWh latent heat released for 8.4 kWh electricity so a CoP of ~ 4:1 --  pretty good, eh?

 

So have I perhaps calculated incorrectly? It has been a busy day. I know it is good and that the chap closing down his drying business recommended those out if all the types he had.

 

Have I misunderstood what they mean by Nominal Current?

 

Spec: http://www.equiplogistics.com/buy/broughton-cr40-heavy-duty-dehumidifier-dual-voltage.html?gclid=EAIaIQobChMIir7HmMn91wIVipTtCh1HsQWoEAQYAiABEgLjpfD_BwE

Edited December 9, 2017 by Ferdinand