toal underfloor heating +HW with solar thermal

[scottishjohn]

Hi,
Ok any one done such a project.
on my present house i fitted 40 thermomax evac tubes +heatstore 20 years ago --this di run the underfloor partially --but the downside was lack of storage
so this time on new passiv or almost sip framed house iam thinking about this again
Ido have a 1000gallon grp tank that ifitted out with input and output coil ,surrounded it with 5"of PIR insuslation ,then air gap and then double bubble foil insulation .kingspan told me that the temp loss from that 5ft x8ft tankwould be around 1.7c per week
this was going to be next step --but wife would not accept me buring it in the garden --so thinking maybe this time to drop this tank or bigger if needed in concrete jacket with pir outer layer in basement of new house .
concrete with have specific heat or at least 4-1. granite is 5-1 so maybe make with granite aggregate so my thoughts are that that will be my thermal mass backup

all thoughts very welcome

[J.P.M.]

Answer : I've done a fair amount of active/passive design/retrofit, but none for quite some time.

From what you write and how you writeit, IMO, uou need an education before you go further. Start with: "The Solar Heating Design Process", Kreider, ISBN # 0-07-035478-2.

You will avoid making as many costly mistakes with more knowledge of what's been done in the past.

[scottishjohn]

you could be right --"every day is a school day" ,so more reading provided you question what you read is good --but If I had listened to thermo solar panel makers +heating engineers 20 years ago they all said what i was proposing then would not work ,but it did to a point of limitation of my thermal store size.I am a great believer in the old saying "those that can DO --those that can,t teach"
same is true of my main business which is motor sports +fast road tuning with rotrex superchargers and that is really all about thermodynamics really

book ordered

[J.P.M.]

John: See my post to your other thread.

Regards,

J.P.M.

[LucMan]

I live and work in NY and it has been my experience that solar thermal works well for domestic hot water production, but not so well for space heating no matter how much storage you have.
The most important issue is solar insolation, how much sun and duration of sun light on the panels. In January and February there is very little when you need it the most. I have records for the last 8 years from my own domestic system to substantiate my opinion.
The size of the array and storage required are substantial and backup will still be required even in todays super insulated homes. In my opinion it's better to go with a solar PV system ( especially if net metering is available) and then use an air to water heat pump in conjunction with low temp radiators and maybe some infloor radiant if concrete floors are used. I have had really good results with Low temp radiators with constant circulation and outdoor reset, it my go to design on higher end installs.

[scottishjohn]

I have no doubt that solar thermal will work --providing you have large enough well insulated heat store which is tall so you get very good thermal separation of the heated water from the cold bottom end so panels can keep filling it up .they have done it in the alps for years --the gable end of the house --20-30ft tall is a tank ,insulated to death on outside - my old syatem had 40tubes heating 300litres --which maxed out with in 4hrs 98c from 17c at bottom after running heating all night -top where hw coil was was still 35c and thats was only 6ft tall, on summers day far too quick even using it to do underfloor --so its just storage size that is the problem --and of course possible legonella if water temps are not cycled high enough --with blank piece of paper -maybe running a cascade of buffer tanks -basically so when in winter you only get enough heat for immediate use you direct it from smaller tank -when thats full heat the next one etc I was going to do that with first system but 20years ago trying to find a suitable controller was the problem --now maybe just link a laptop to it and correct software --hope there is suitable software out there already to control valves and temp sensors+pumps etc.
for a retro fit very few houses will have the space need for enough storage --but new build with basement --thats the way -maybe the concrete basement is the storage tank ?
I know how much heat I can get in scotland because a sensor failure caused it to keep running and it melted the foam insulation from 20 metres of copper pipes --that means at least 170c to melt plastic foam .as for back up if you ran out of hot water --an inline electric heater like this https://www.heatraesadia.com/product...roductgallery2

[J.P.M.]

I have no doubt that solar thermal will work --providing you have large enough well insulated heat store which is tall so you get very good thermal separation of the heated water from the cold bottom end so panels can keep filling it up .they have done it in the alps for years --the gable end of the house --20-30ft tall is a tank ,insulated to death on outside - my old syatem had 40tubes heating 300litres --which maxed out with in 4hrs 98c from 17c at bottom after running heating all night -top where hw coil was was still 35c and thats was only 6ft tall, on summers day far too quick even using it to do underfloor --so its just storage size that is the problem --and of course possible legonella if water temps are not cycled high enough --with blank piece of paper -maybe running a cascade of buffer tanks -basically so when in winter you only get enough heat for immediate use you direct it from smaller tank -when thats full heat the next one etc I was going to do that with first system but 20years ago trying to find a suitable controller was the problem --now maybe just link a laptop to it and correct software --hope there is suitable software out there already to control valves and temp sensors+pumps etc.
for a retro fit very few houses will have the space need for enough storage --but new build with basement --thats the way -maybe the concrete basement is the storage tank ?
I know how much heat I can get in scotland because a sensor failure caused it to keep running and it melted the foam insulation from 20 metres of copper pipes --that means at least 170c to melt plastic foam .as for back up if you ran out of hot water --an inline electric heater like this https://www.heatraesadia.com/product...roductgallery2

Sure iyt'll work. Whether or not it's fit for purpose or cost effective are separate questions. See my post to your other thread., Re: storage, etc.

[Mike90250]

here's a good writeup and followup on a solar hot water system in frozen north

https://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm

They have cold, and sun, no sun = no nothing
SW Montana at 46 degrees north latitude. Winters are chilly -- 8000 degree-days and down to -30F once in a great while

[J.P.M.]

I don't want to rain on this guy's parade - I probably couldn't have done as good a construction job, but in the battle of common sense over the urge to build stuff it looks like common sense lost out. It's always easier and less expensive to reduce a heating load than to provide more heat via solar by most any method. Conserving after a well designed and optimum solar retrofit only makes the retrofit less cost effective by making it oversized.

I'd also like some information on what it cost, including some value for labor, to not use the propane as claimed.

[LucMan]

His Montana published results spell it all out 240 sq ft of collectors producing 160,000 BTU per day the equivalent of 2.2 gallons of propane! A couple of 8ft glass sliding patio doors on a south wall of the house would give the equivalent results.

[scottishjohn]

my latitude in 55-
no more thoughts now till i get final house design and heat claculations done --I think you could be right that air source heat pump ,as i have in my present house
will work out cheaper overall with RHI grants aviailable. which will pay back 60% of system in 6 years ,

down side is I have it fitted by approved engineer to get RHI grant