New system design...Help required

[David-Robo]

Hi Guy's,

I am just coming to the end of a self build project and am now at the stage where I need to fit the solar thermal and PV. The problem is that the solar thermal design is not a standard design as it is not only going to be supplementing a Vanvex RS DHW air to water heat pump. But it is also going to be providing heat for the UFH and towel rails. I am told that I don't actually need the UFH as the house is built out of ICF to a U value of .15 Which I am told is passive house standard. It also has a Genvex premium L1 MVHR with an inbuilt air source heat pump. Which alone should provide all the space heating requirements. But as I went for this unit I had to find a solution for the DHW. Which I didnt want to use an electric boiler for as I didnt want to be at best getting 1 to 1 power for heat. I liked the idea of a Co-op of around 3-3.5 by using heat pumps etc.

It is only now after looking through the forum that I came across the threads done by qeipl regarding the ecocent unit with the built in UFH coil. Which would have made my life a million times easier.   But you learn from your mistakes, an I know for next time.

I have done 3 different designs so far. I will post them one at a time and welcome any feed back or criticism about the designs. The third will be the one which I plan to implement all being well.

The first is this one:-

[David-Robo]

The second is this one:-

[David-Robo]

An the third is this one:-


I think that this one is the best as it simplifies things a lot and it negates the need for a second coil in the thermal store tank, the need for additional pumps and also I think it gets the most out of the system all round. I did toy with having the 20 tube panel connected to the Vanvex and the 15 tube one connected to the thermal store. But I think the 20 tube isn't quite enough on it's own to do enough in winter. Plus in summer it would blow off a lot I think. Where as in series they would work together to heat the Vanvex, then once up to temp they would quickly heat the thermal store. An only then would a dump in the loft need to be activated.

So any comments or suggestions would be greatly appreciated. As I plan on ordering all the stuff this weekend.

Kind regards, Dave

[Drawmer]

I've hesitated to answer this, since there are many Guys and Girls on here with more knowledge and experience than I have.

However (you knew that was coming!) I think that any attempt to use solar for heating as opposed to DHW is not going to be efficient. The problem is, even with a super insulated house, you are going to want more heat energy exactly when the system will struggle to provide it in the short dark days of winter.

If you upsize the solar panel to cope, it will add to the installation cost, and mean much more heat is dumped when the sun is high and the days are long.

I think that to do anything effective with solar and use it to supplement domestic heating you will need far more tubes than you are planning on using. It can be made to work, but in my amateur opinion it would be satisfy aesthetics more than be cost effective.

There are just two of us here, and our system is only for DHW. With disciplined use, it works fine for 5 months of the year, in reality we should have 50% more tubes. (system details in signature)

[David-Robo]

Hi Drawmer,

Firstly thank you for your reply.

I understand what you are saying as I have heard this said many times. However I have also heard people say that it can be used to supplement the heating in a well insulated house. An by that I always assumed that it meant modern standards I.E. A U value of say .28 or .2 but with a U value of .15 no actual heating is required. The heat from lighting, cooking, body heat etc should be sufficient to maintain the temp of the house. To give you an indication of just how good it is. We put the roof on and windows in in November when the temp was -10 on average. It was only 4 weeks ago that you could no linger see your breath in the house. Ad the temp remained so low due to the insulation. It is only now the scaffold has come down that it has allowed some direct sunlight into the house that the temp has finally increased a little.

I have a friend who has 3 x 20 tube 47mm panels with a 215l cylinder and on an overcast October morning at 10am his tank was at 45C. He assured me that it would be at 55C by dinner time and that was without direct sunlight. So my thought are that there should be some heat for the tank even in winter.

To be honest it is not so much about providing heat for the UFH as I don't think it will really get used. It is more about heating the DHW tank and towel rads. We only have the output of the second cylinder blended down to 55C in case the UFH ever does Get used. That way the towel rads and UFH can be on the same pipe work. an if the UFH is in use in winter and the tank isn't hot enough the immersion heaters will come on to raise the temp to around 35C which is perfect for UFH. What I'm trying to do is make the house be kind of ticking over consuming a small amount of electricity to power all these devices so that there is little or no export. That way all the elec produced by the PV will be energy saved at around 10 pence per KWH, rather than energy sold at 3.3 pence per KWH. Also this is an experimental build that has incorporated tech which most people still haven't got their heads around. So the data collected regarding how the house performs will be used to aid in the design if future properties. Plus there is much more roof space than what is already ear marked for use. I could easily expand the evacuated tubes or PV if it is under sized.

Kind regards, Dave

[dhaslam]

For underfloor heating from  solar you would need a separate system. The DHW controller is always going to  try and produce hot water, so on a dull day in winter  it won't  produce much unless the DHW cylinder is very cold.   A dedicated heating system can start transferring heat as soon as the output is warmer than the floor and it can stay running  quite a lot even on a dull day.  It would however need some form of storage to get the best from the system  and in summer it would need an alternative use.


A very well insulated house still needs some heat input.  South facing rooms will get heat from the sun but north facing rooms will need quite a lot of heat, several hundred watts, to compensate.     

[David-Robo]

Hi dhaslam,

Thanks for your input.

I have a friend who has built a similar house but at a U value of .2 as oppose to my .15
To this day he has only used his underfloor heating twice. Once to dry out the plaster, An then again to dry out the paint.

The solar controller would only know the temp of the heating tank. As the DHW tank will be separate from it entirely. The DHW tank will have a have a sensor in the panel and a relay which would normally activate a pump connected to the inbuilt controller. An when the panel has any heat it will try to activate a pump but instead will activate a motorised valve which will divert heat into the DHW tank until the DHW tank is up to temp. However the Solar circ pump would not be active if there is no heat in the panel as the TDC controller will also be connected to the panel and will have a sensor in the heating tank. So when there is heat it will activate the circulation pump and the heat will circulate. If the heat pump has already brought the DHW tank up to temp the the heating tank will receive the heat. However if it is cold then the heat will instead flow into the DHW tank.

Does anybody see a problem with this set up?

Kind regards, Dave

[Justme]

I am in the middle of fitting a 30 x 58 tube system to replace out 20 x 58 tube one (different types).

Whilst our current one does provide most of our DHW for under half the year & help in the rest we estimate that the new one will do 100% for over half the year & help for the rest.

I think I am right in saying that in full sun the 30 x58 tube array is capable of making 1.5kw's of heat. So over a full 8 hour sunny day the most it can capture is 12kwh. In winter I would guestimate that at more like 2 to 4 kwh per day.

So at best you are looking at 5kwh per day. Thats not going to raise the temperature of your 150L tank by much.


What is the heat loss / demand for your house?

Quoting a U value of 0.15 does not help if its 2000m2 in size

[David-Robo]

Hi justme,

LOL yes of course! sorry I didnt even think to include that. The warm part of the house is about 132M square. So the heat demand is very low. I don't know how well versed chaps on here are with regards to the performance of construction materials. But I spent years researching the subject before deciding on ICF. As ICF may on paper (SAP calculation) perform the same as a house built from brick and block with the equivalent U value. But in reality it will far exceed it. Due to the air tightness, Thermal mass, decrement time and of course the insulation it's self. Not to mention the fact that I opted for a Finnish of partially brick slipped and partially rendered. So there is no cavity to hinder the thermal performance of the building.

Only time will tell really. But as far as I can tell, the house doesn't need any form of heating. So ANY heat which I can add via the UFH will be a luxury item as opposed to a necessity.  In future builds I plan to incorporate some sort of remotely activated shutter system to shield the panels from the sun in summer. Therefore enabling the system to be significantly over sized. An to anyone who says that the extra panels would cost a lot more. All I can say is after seeing some of the quotes I had for a ground source heat pump with bore hole! 10 panels would still be cheaper lmao.

What you say about the amount of KWH's the system will produce is a bummer really as it is the most annoying thing about solar heating. When you need the heating there is no sun an vise versa. The 5 KWH's would all be going in to the DHW tank no doubt in winter. I doubt there would be any spare for the heating. I could however change the program on the DHW controller so it wouldn't use the solar sensor and relay. Therefore giving all the available heat to the heating. I would of course still benefit from the heat pump on the DWH side of things. Which is I guess better than using the immersion to heat the heating store and using the solar for the DHW. When you say 5 KWH's I imagine my 2.4KW kettle which will boil 2L of water in about 3 min. So 2 kettles would no doubt do the same volume in 1.5 min. Based on this I would imagine that the 5 KWH's is the same as having 2 kettle's boiling away for an hour! surely this should be able to get 150L up to a reasonable temp. As it should be able to boil 80L based on the same calcs would it not?

Kind regards, Dave

[Justme]

Using your 2.4kw / 2L / 3mins from 10c to 100c example I would guestimate that 5kwh could raise your 150L by 48c IF you had no system losses at all.

I dont know how accurate that is. I dont think we see a 48c rise in one day in summer (ok 20 tubes & 200L) never mind winter.

[David-Robo]

Hi guys,

Just to update regarding the insulation performance etc. The house is still not finnished due to budget issues. But it's now nearly at the Finish line. I've just fitted 2.5kw of pv and my solar thermal system is being fitted now. But I have had the heat recovery running since the beggining of summer. The house has had no form of heating so far at all and the loft hatch has been left off. Not to mention that the garage door and front door have been left open all day when the workers have been on site.

Yet in spite of all this the temp inside is still around 13C so I'm very hopefull that once the house is occupied and it has been heated up to temp I think it will retain it's heat all year round just from body heat, cooking and baths/showers etc. So I think that with the FIT and RHI the house will pay for it's self utility wise and then some.

Kind regards, Dave

[kalas666]

Hi, just to give you something to think about, below is a schematic of my system.
Basically the boiler is set to run for an hour in the morning and heat the top third of the TS in summer, and 2 thirds in winter to 50 Deg.
This means that in the summer the solar can contribute as much as it can.
Also means the the log boiler can supply the energy when lit.
If there is no Sun and no Logs then the boiler can do the lot!!!

P.S 475Ltr store

Chris

[micko]

 Hi,
A little off topic but could I ask what software you used for that last diagram. 

[bornagain]

Hi David-Robo

For what it's worth, we built our own 190m2 ICF house during 2011 and moved in late October; we also have a U value of 0.15 (Beco 375 system), floor slab is on top of 300mm of EPS, 600-700mm of glass fibre in the loft - probably a similar spec to yours ??

We have triple glazed doors and windows, quite a lot of south facing glass and a fairly standard MVHR unit.

We made a big deal out of the concept of thermal mass- 1st floor is beam & block, all internal walls are wet plastered blockwork.

We have PV, Solar Thermal (4.32m2 of ET) and a  small room sealed woodburner, both  connected to an 500 litre Akvatherm Solar Plus Thermal Store; the store also has two 3KW immersion heaters.  The thermal store is connected to downstairs UFH.

We have no heating upstairs, not even the bathrooms.

I debated all manner of heating options - ASHP, GSHP, Big Solar Thermal, Gasifying wood boiler blah blah blah.  Our experience so far, part through a fairly mild winter (but with some cold days and nights, -5 C being the coldest morning) is that the heating demand is very,very low.

I am a Mechanical Engineer (and therefore pretty geeky with the sums) so played around with Excel doing all manner of modelling which has turned out to be reasonably accurate, ICF does appear to perform roughly in accordance with "what it says on the tin"

We are a pretty standard family, 2 x adults, 12 & 15 year old boys and I assume our use of electrical devices is about average so that should give you some idea of the heat we generate just living in the house.

We have found that there is very little practical need to use the woodburner, but it is very tempting to light it as the ambiance that it provides is lovely, and it does have the benefit of heating up the north facing living room and allowing heat to enter the hallwayand make its way upstairs.

In retrospect;-

What we (I) got wrong - we should not have bothered with UFH, its lovely when its on, but is on so infrequently that it's not really necessary and adds to cost and (to some extent) complexity - electrical panel or possibly E7 storage heaters would have been quicker/cheaper/easier. 

What we got right -not bothering with fancy ASHPs, GSHPs, Huge Solar Thermal etc etc - it's all too complicated and is asking to go wrong. Lots of south facing glass makes a big difference. We fitted low flow shower taps and shower heads - this appears to have helped reduce the DHW demand.

I expect an electricity consumption of around 6-8000 kWHrs/yr as our only fuel bill, we should clear £1500/yr from the PV so we will have a net negative energy bill.

I hope this helps, but its probably a bit late...If you have any questions then don't hesitate to drop me a message..

Enjoy !!

P.

[David-Robo]

Hi Guy's,

Thanks for the info guy's its really appreciated. I agree with you P. regarding the UFH. everyone I spoke to said that it would never be used. An with the Genvex as well I doubt it will be used at all.

Next time I want to try and have an underground duct for the intake air and use an ecocent as an exhaust air heat pump. Then I can connect the UFH and towel rads to that and not have to have the genvex or the thermal store. I could connect the solar directly to it so not having to make it over complicated.

Kind regards, Dave