mvhr and minimal other heating

[scottishjohn]

unless they change things after the RHI grant stops for PV i doubt it will be viable any more --time will tell.

ASHP has everything beat at this time 

I have a mitsubishi plumbed cylinder unit on my heat pump on current house -which is why i dumped solar ,as the anti legonella function knocks tempup to 60c every now and then which makes best use of solar in moderate months not that good .i have alot of experience over the years with solar thermal and it all revolves round getting as much out of it when its day light ,so lifting tank temp up by other forms stops solar working for a lot of hours .

good control of what does what is needed to get best form it--simple dhw only --you just want a big tank 

i used blender on dhw supply so i only took minimal hot water from tank at 45c after cold blend  --no point in putting lots of cold in it at the tap 

my tank ahd dhw coil at top UF in middle and solar coil at bottom and boiler heated parent volume when solar could not or UFH demand was too high for solar

cop when raisng dhw to 60c is not good --

what i can say is when i swopped from modern lpg boiler to ashp i saved £1300 a year --house is not up to modern insulation stds add that to RHI and ashp is no brainer even on an older house if no mains gas --if you have rads then they need to be changed for ones designed for heat pumps

[Jeremy Harris]

A few points worth noting:

 

Opening windows in hot weather makes the house warmer - better to keep them closed during the day and let the high decrement delay of the structure limit the increase in internal temperature.

 

Solar thermal is significantly more expensive than PV, especially if the PV is built in to the roof, so saves slate and roofing cost.  It's better to fit PV, even with no FIT, as it's cheaper, and you can use the electricity not just for heating water, but also running other stuff, too.

 

Hot water storage can present problems; we found that our services room got to over 40 deg C when we had a double insulated thermal store in there and heat leaked from there to the adjacent bedroom, getting that room to over 30 deg C.  In the end I swapped the thermal store for a Sunamp, with around 1/4 to 1/3 the heat loss, which made a massive difference in the warmer parts of the year.

 

RHI won't make any sense for a low energy house, as the payments will be tiny.  In our case the payments for our ASHP installation would have been only £84 a year for 7 years, which was far less than the additional cost of having a certified ASHP install.

 

 

[scottishjohn]

I had this heat leakge problem with the tank when first supplied,as the foam used was rubbish 

i got PIR steam pipe lagging pipe sections and put them round tank --problem went away .no dhw tank is supplied with enough or correct insulation they are made to a price ,so they use low grade foam that is pumped into jacket

,even old style copper tanks which do  have proper type of phonelic or PIR  insulation on them ,are not good

they need extra  and include all the pipes coming out from tank ,if you want to keep heat in right place .

physics tells us that making electric to then use it to heat water has to be less efficent than diret use of sun ,you are just trying to make use of PV electric that way and if no FIT --that don,t make sense--

anyway time will tell with what happens after FIT is stopped  if it is not replaced by something else

I can,t see how fitting pv in new roof will save on slates  as you have to have something there instead 

if its cost then you do not use slates at £9-15 per slate for welsh slate

at 19slates sqm that is lots of money £170-£285sqm

 use concrete tiles at around  £1 each which equates to £10sqm or recycled concrete /slate mix at £20 sqm

yesI,m a scot --every penny is a prisoner

how much is a recessed pv roofing panels per sqm

Edited November 12, 2018 by scottishjohn

[Jeremy Harris]

I added 50mm PIR, plus loads of expanding foam, around our old thermal store, and the thermal store was supplied with double insulation, by special order.  As delivered the heat loss was well over 3 kWh/24 hours.  After adding the insulation I got it down to a bit over 2 kWh/24 hours.  The Sunamp loses about 0.7 kWh/24 hours, so is massively better.  There are thermal images around here somewhere from the time I was having this problem.

 

We saved around £2k in roofing cost by not having slates under the in-roof PV, so that effectively made the PV panels around £2k cheaper than if we'd fitted them on the roof instead.  The cost difference between in-roof and on-roof PV is small, and in-roof looks a great deal better IMHO:

 

 

Do the sums and see what the cost of a PV install is versus the cost of a solar thermal install.  @Ed Davies has done a fair bit of work on this in the past.  PV panels have reduced in cost a great deal, whereas solar thermal costs haven't come down at all.

[scottishjohn]

your point on not using certifed ainstaller is noted anf filed away .

do you use ashp for hot water as well as PV.

 

[Triassic]

4 hours ago, Onoff said:

 

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

I for one just wish that volume house builders would build the majority of new housing stock to a decent standard.

[scottishjohn]

1 minute ago, Triassic said:

I for one just wish that volume house builders would build the majority of new housing stock to a decent standard.

and air test should be done before dry wall is fitted--and not just seal up the skirting boards.

Iwill certainly be doing my air tests at that stage

[Jeremy Harris]

4 minutes ago, scottishjohn said:

 

do you use ashp for hot water as well as PV.

 

 

Yes, I have a small buffer tank (70 litres) that's heated to 40 deg C by the ASHP (which means the ASHP runs efficiently) and then I use a plate heat exchanger and flow switched pump to pre-heat the incoming cold water to around 35 deg C to 40 deg C before running it through the Sunamp heat exchanger, which boosts it to around 55 deg C, using heat stored from excess PV generation. 

[scottishjohn]

I understand why you do what you do --"seems a long way for a short cut" and complicated when one solar thermal will do so much more 80%of the year minimum to a much larger volume of a tank and a very simple control system 

maybeyou would get  more where you are --but it does 80%+ in scotland  no problem  and htat was when we has 2 girls at home --now just the 2 of us even easier

[Square Feet]

Can anyone give me a ballpark figure for installing UFH pipes into the slab during construction?  Just a very rough guide please?

Cheers

Edited November 12, 2018 by Square Feet

[ProDave]

There are very many ways to tackle a low energy house and you cannot say one is right and the others are wrong.

 

We are in the Highlands a little north of Inverness. We are in a sheltered glen far enough inland that the sea has little influence, and a couple of weeks in winter when it sits at -10 is not uncommon.  I very much doubt any house would work well with no heat input at all in that so UFH is a must as far as I am concerned.

 

I have opted for a small 5KW ASHP heating UFH downstairs only (and just bathrooms upstairs) and also doing the bulk of my water heating. Even if you only need say 3KW a little larger is better as it will run at a low level rather than running flat out.

 

I find the heat loss from an UVC to be tolerable it seems they might generally be insulated a bit better than a thermal store but obviously not as good as a Sun Amp for instance.

 

I will be fitting solar PV to try and cut down my electricity bill.  So far space heating and  water heating is a minor part of my electricity bill.   Other "stuff" uses more, thinks like the dishwasher, washing machine, tumble dryer, fridge/ freezer etc. So anything that can help power those will be a big energy saver. The ability to use surplus to also heat hot water makes it even better.  Solar thermal would not work for us due to so much shading from trees so it could not go on the roof.  You can mount PV remotely from the house to overcome that, but solar thermal would not work mounted remote from the house.

 

If however you are using solar thermal, then turn off any legionairs heating function, let the solar thermal do that. But we had a discussion about that and under certain circumstances there is no need to do that anyway.  

[Pete]

6 minutes ago, Square Feet said:

Can anyone give me a ballpark figure for installing UFH pipes into the slab during construction?  Just a very rough guide please?

Cheers

 Are you doing the work? If so you can work out the pipe spacings and how much pipe you will need if you use Loopcad which I believe is free for a month. We did all this and then fitted the pipes to the steel mesh one Saturday morning so it only cost us materials. Each build will be different as the square meter cost will differ for each house but it is definitely very easy to do and is well worth having it in the slab as a fallback if you decide you need UFH later. I would say on average it costs between £500 to £1000 for materials which includes pipe,manifold,pump etc and cable ties depending on the size of the property.

[Declan52]

13 minutes ago, Square Feet said:

Can anyone give me a ballpark figure for installing UFH pipes into the slab during construction?  Just a very rough guide please?

Cheers

The price will depend on how much pipe you need and if your doing or a trade.  More pipe more expensive.  You can get 500m rolls for  £300 or less so work out if you need 1,2,3  rolls and then after that it's only clips.  You won't need manifolds and pumps when you are doing the slab. 

There is a pipe decolier in the  tool hire section which if you are doing it yourself will be  a lifesaver. 

[Square Feet]

3 minutes ago, Pete said:

 Are you doing the work? If so you can work out the pipe spacings and how much pipe you will need if you use Loopcad which I believe is free for a month. We did all this and then fitted the pipes to the steel mesh one Saturday morning so it only cost us materials. Each build will be different as the square meter cost will differ for each house but it is definitely very easy to do and is well worth having it in the slab as a fallback if you decide you need UFH later. I would say on average it costs between £500 to £1000 for materials which includes pipe,manifold,pump etc and cable ties depending on the size of the property.

 

Thanks Pete, that is useful.  Yes I would do the work myself, sorry, I should have said that.  I will stick it in the budget for £1000 and hopefully that will do it.

Cheers

[Square Feet]

1 minute ago, Declan52 said:

The price will depend on how much pipe you need and if your doing or a trade.  More pipe more expensive.  You can get 500m rolls for  £300 or less so work out if you need 1,2,3  rolls and then after that it's only clips.  You won't need manifolds and pumps when you are doing the slab. 

There is a pipe decolier in the  tool hire section which if you are doing it yourself will be  a lifesaver. 

 

Nice one, thanks. I'm just at the budgeting stage atm, but I will bear that in mind.  Cheers

[Declan52]

10 minutes ago, Square Feet said:

 

Nice one, thanks. I'm just at the budgeting stage atm, but I will bear that in mind.  Cheers

The only thing to watch out for is if you aren't connecting all the pipes up to a manifold and have the  pipes sitting under a few bar of pressure you run a greater risk of the pipe being damaged during the pour.  People here have done it both ways so it's up to you.

Not sure how your plumbing skills are with regards connecting all the pipework up to a manifold but even if it's only a few hrs work  for a plumber it might be money well spent. 

[Square Feet]

5 minutes ago, Declan52 said:

The only thing to watch out for is if you aren't connecting all the pipes up to a manifold and have the  pipes sitting under a few bar of pressure you run a greater risk of the pipe being damaged during the pour.  People here have done it both ways so it's up to you.

Not sure how your plumbing skills are with regards connecting all the pipework up to a manifold but even if it's only a few hrs work  for a plumber it might be money well spent. 

 

I'm a reasonably competent diy plumber.  I have plumbed in bathrooms and kitchens before, but not done much messing with central heating. Thanks for the tip re the pressure.

Edited November 12, 2018 by Square Feet

[Triassic]

39 minutes ago, Square Feet said:

Can anyone give me a ballpark figure for installing UFH pipes into the slab during construction?  Just a very rough guide please?

Cheers

I cost me the price of the ufh pipe (around£600) and a day of my time to install it. I zip tied it to the steel mesh prior to pouring the concrete. I used a free ufh layout package to work out the optimum pipe layout and length required.

[Jeremy Harris]

2 hours ago, scottishjohn said:

I understand why you do what you do --"seems a long way for a short cut" and complicated when one solar thermal will do so much more 80%of the year minimum to a much larger volume of a tank and a very simple control system 

maybeyou would get  more where you are --but it does 80%+ in scotland  no problem  and htat was when we has 2 girls at home --now just the 2 of us even easier

 

The main issue is the cost, IMHO.  You pay a lot more per kWp output for solar thermal than you would for PV, and solar thermal stops delivering any benefit at all after a couple of hours of heating the hot water storage system.  PV is both cheaper and saves you money on your electricity bill, as well as giving you hot water.  PV will also start to heat hot water when the energy input is low and the storage system is quite warm, but not hot, when a solar thermal system won't start to deliver heat until the collectors are hotter than the storage system.  There's also zero maintenance for PV, whereas solar thermal needs a circulating pump, special antifreeze/inhibitor (that has to be changed every few years), etc. 

 

Worth looking at the useful information that @Ed Davies has put together, comparing the cost vs benefit for the two options: https://edavies.me.uk/2012/11/pv-dhw/ (bear in mind that PV cost has reduced a fair bit since Ed wrote that, whereas solar thermal costs have either increased or remained much the same as they were, as it's become less popular, probably because of the fairly large cost difference per kW when compared to PV.

[scottishjohn]

thanks will give this a look

[scottishjohn]

bit hard to get real comparison as no heat output given or even staed on navitron site for evac tubes  and as istated earlier the key is having enough storage so panel never gets to stagnation point in a day .

will  look again later when fulldesign specs are available for house 

all information is good  and added to the pot for cogitation 

prices for solar thermal are now much lower  and a 3sqm panel can be be under £500 --your solar pv is 250-350 for 325watts

solar thermal when enough sun from that one panel will be 1800w,quoted kingspan thermomax 30 tube panel spec,

so all depends on how much free power with pv you need to use i suppose and how much hot water you need 

never simple 

 

Edited November 12, 2018 by scottishjohn

[scottishjohn]

the advent of cheaper pv storage  could make a big change ,but costs at this time --a bit iffy 

[Jeremy Harris]

IIRC, evacuated tubes have an efficiency of around 60% to 70% (might be wrong, been a while since I've looked at the specs in detail).  The output can then be derived from the insolation, in much the same way as for PV.  The difference is mainly that the output of a solar thermal system reduces as the temperature of the storage system increases, whereas the output of a PV system remains the same irrespective of the temperature of any storage system.  One effect of this is that PV will deliver energy earlier and later in the day than solar thermal.

 

2 hours ago, scottishjohn said:

the advent of cheaper pv storage  could make a big change ,but costs at this time --a bit iffy 

 

Makes no difference if all you're storing is heat.  In my case the Sunamp charges up from the PV and stores that heat pretty efficiently, so that heat can be drawn off as needed hours, or even days, later.    Once the Sunamp is recharged, then the PV generation just reduces our electricity bill, and for a fair part of the year there's enough excess to keep my car charged up too, which saves even more money.

 

Batteries have a fair way to go before they make sense as affordable energy storage at a domestic scale though.  The cheapest systems currently available will never pay for themselves in terms of reduced bills from using grid electricity; they will almost certainly reach the end of their useful life several years before the investment has been recovered. There may be other reasons for fitting such a storage system though.  We suffer from fairly regular power cuts, and the option of having 3 kW of emergency power available (which comes as standard on one of the more affordable systems) is appealing.  The question is really how much we're prepared to pay for the convenience of being able to keep the lights and TV working.

 

 

[Guest Alphonsox]

5 hours ago, Pete said:

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

 

Unfortunately I haven't lived in the place for a long enough period to have gathered that information. All I can say at the moment is that the house is reaching a comfortable 20C by using only the immersion heater running for a maximum of 7Hrs/Day even in the coldest periods.

[Nickfromwales]

4 hours ago, joe90 said:

 

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.

Back up is one thing, so that was not aimed at you, it’s for those who have underestimated the ‘need’ for heat and how to best deliver it, both comfortably and conveniently. 

Having to employ auxiliary heating should be the exception not the rule at best.