Dual heat store design help please!!!

[aberborthin]

Hi Everyone,

As a newby I am posting for the first time looking for either help or suggested threads to look at....

My planned system and thoughts..

- Fully renovating an old Welsh Long house
-  5 sq mt solar panels
- 2 wood burners with back boilers (Clearview 650 and Nordica)
- New extension (garden room with slate roof 5mt x 7 mt)
-  UFH to kitchen, garden room and down stairs bathroom
-  Rads in 2 upstairs beds and bathroom
-  Not lovers of over heated houses
-  Nordica in kitchen to provide background heat and heat thermal store (stairs lead off kitchen and heat to warm upstairs - rarely used)
-  Solar to provide hot water in non winter months
-  Clearview in garden room to provide extra heat to room and thermal store

I had hoped to install a TiSun 500l thermal store but only suitable location has sloping roof and its too tall!  I also have a width problem with doors and stairs to ideally need a tank that has detachable insulation.

My idea now is to use 2 thermal stores (250 -300l each)  with some clever coupling system so that in the summer the solar panels will heat one for our hot water and in the winter the back boilers (+ solar when available) will be able to heat both.

Anyone have suggestions to the design of this system??

[dhaslam]

There a are quite a few questions
 Are the two stoves close together enough to heat a pair of tanks in the same place?
Will one stove be used more than the other?
Do you want to use a direct mains system for hot water i.e with coil in store or stores?
Could you make space downstairs for one big store in a place where both stoves could feed it by gravity? 

[wookey]

Consolar and TML both make large tanks with removable insulation. In general a system with one large tank is better (lower losses) than one with two small tanks, but both arrangements be made to work. See the navitron tanks wiki page for basic info: http://www.navitron.org.uk/pmwiki/pmwiki.php?n=SolarThermal.Tanks

[aberborthin]

There a are quite a few questions
 Are the two stoves close together enough to heat a pair of tanks in the same place?
Will one stove be used more than the other?
Do you want to use a direct mains system for hot water i.e with coil in store or stores?
Could you make space downstairs for one big store in a place where both stoves could feed it by gravity? 

Much of my problem is the cottage itself - floor strength, joist depth, old oak walls and the general layout! - still it is all these things that attracted us to the cottage in the first place....  There is really only one place for the tank(s) where I can get 28mm pipework and keep hot water run lengths to a minimum - as it is this area will still need some floor strengthening.

The Nordica boiler is new and very efficient - will heat a tank from cold and cut in and heat the rads in about 40 mins from lighting and the Clearview will be used to boost output in cold weather.

I appreciate that one tank would be more effective than 2 generally, but space dictates I can not fit one tall tank.  With only 2 of us in the house, I am also thinking that one smaller tank in the summer will prove quite efficient.

[lightfoot]

Good Morning Aberborthin,

Have you considered using just one WBS with a back boiler, to supply (via a thermal store) the rads/UFH and DHW (or even a automated pellet stove and DHW cylinder/smaller thermal store) - then having a stand alone (room heating only) WBS in the other room to augment the CH etc.  

Or even, depending on your needs, you could also consider using a high efficiently dedicated log batch or pellet boiler in boiler room etc.

Akvaterm offer detachable insulation as a option... http://www.akvaterm.fi/?tocID=3

Anyway, for some more info, ideas and options, you may want to pick the bones out of these threads (you'll find more if you do a search - enough to make your eyes bleed )....

http://www.navitron.org.uk/forum/index.php/topic,4547.0.html

http://www.navitron.org.uk/forum/index.php/topic,4433.0.html

http://www.navitron.org.uk/forum/index.php/topic,4110.0.html

http://www.navitron.org.uk/forum/index.php/topic,5147.0.html

http://www.navitron.org.uk/forum/index.php/topic,8559.0.html

http://www.navitron.org.uk/forum/index.php/topic,8611.0.html


Hope that's some use,

Lightfoot.

[dhaslam]

I think your best option would be to use the two cylinders and to set them up so that one is normally hotter than the other.   If you run the heating off the cooler one and perhaps use the better stove to heat it. The other could run  from solar and the second stove.   The solar conteroller will have the ability to transfer heat to the second tank when necessary and also with the proper controller it can top transfer heat the other way.    Note that the floor will hold heat for a long time so there can be a bit of flexibility with space heating. The DHW will need to be heated constantly so it is useful to have an immersion on night rate well down in the cylinder for days when you don't want to light the stove.   Note that the two stores need to be very well wrapped up because the heat will be lost into the attic.

I have a separate store heated by heat pump and stove.  The DHW cylinder is heated by  solar, heat transferred from the store and by immersion.    I need to separate the store into hot and cold layers  so that the hottest water on the top only goes to the other cylinder.   The underfloor heating should have had a separate outlet lower down.   Having separate tanks is quite good.  Underfloor heating will still work right down to about 25C so it would have a 40C range to work with.   The DHW store has to be kept at higher temperatures.   

[aberborthin]

Hi,

Many thanks for you thoughts and links which I will now work my way through...

Lightfoot - I already have the 2 log burners and would be very reluctant to change them as they both work very well.

Stratification is an issue that I feel has to be solvable by the Themal store manufactures, indeed if I understood the TiSun info correctly, their tank does send the hot water to the upper part of the tank until it is hot then feeds the middle and then the bottom.  To my mind this means that if I get a short period of solar I will at least get a part tank of usable hot water rather than a whole tank of warm water.  Given our usage can be limited and indeed focused on "free" hot water days, I believe that this would be a more efficient system ( not suggesting that we do not wash on cloudy days... but baths rather than showers and heavy duty kitchen days - pickling, baking etc - could be programmed for when hot water is available) 

To me the system would:

1.  Heat tank 1 from solar when available from the top down
2.  When tank 1 at full temp solar would switch to tank 2
3.  The back boilers would heat tank 2 and feed UFH "overflowing" to tank 1 if no solar
4.  In Summer when solar not available, we have tended to light the kitchen stove for an hour to heat a tank of water so I guess I would need to be able to direct either which tank the heat goes to or be able to draw HW of either tank


Some of this could be does by auto valves and some by manual switching...

All sounds straight forward but as I am not a heating engineer I guess it would....

Anyone fancy trying to design such a system??  or know someone who has???

[dhaslam]

That makes reasonable sense except you need to ensure that DHW does get priority from the stoves.   Normally stoves will heat the store from the top so here should be a layer of very hot water at the top.   This needs to be reserved for the DHW tank top up.  UFH take off can be just below it.   There are a couple of points about the interconnection between the two tanks.   The transfer to the DHW tank needs to go into the top, ie top of tank A to top of tank B  with a return lower down.  The transfer from B to A  (excess solar heat) should go from fairly high up in tank B.   To do this and stop unneeded circulation it probably means a  coil fairly high up in tank B (DHW) fed with raw water from tank A and the same coil and pump could transfer (excess solar) heat  back.   

[lightfoot]

What's the total floor area of the house and do you have any idea what the peak (mid winter) heating load will be ?

What's the output, both to room and water, of the Nordica and also the Clearview 650 (or which of the three boiler options is fitted at the moment - which, if you wish can be changed/removed) ?

You mention that you already have the two stoves and that they both work really well - are they installed and how is the system set-up at the moment, or have you just brought them form another house ?

Do you have a good mains water supply (pressure & flow-rate) and are you in a hard water area (do you suffer with limescale deposits) ?

[aberborthin]

Thanks both for your continued interest from this amateur heating designer! 

The Nordica stove (6.5 kw I believe with 80% going to HW) will be reinstalled in the kitchen.  The clearview will be moved into the new extension 5m x 7m with a vaulted roof, and I have yet to decide on which of the three back boilers to install, it has been suggested that the smallest would suffice.  I appreciate that the area of the house is a fundamental when calculating heating requirements, however, as stated, we are not looking for heavy duty CH as we both prefer a cooler atmosphere.  We have now survived 5 winters (one hard) with the Nordica providing background heat, hot water and warm rads upstairs.  The clearview heated the existing sitting room (5m x 4m) albeit not running anything like max chat.  I would estimate downstairs footprint = 90 sq m with the upstairs 2 bedrooms/bathroom approx another 40 sq m. Additionally we have a small clearview woodburning stove which we plan to put in the existing sitting room.   Excellent water pressure - 25mm supply, soft water area. 

No gas available and we don't wish to install either gas or oil tank (hoping to buy local woodland to supplement wood store).

Whole cottage is being ripped to bits, all existing plumbing and electrics being replaced.  The extension will have building regs plus insulation and the rest of the cottage will be insulated to a high standard.  The whole property should match current insulation requirements as for new build (albeit with the odd weak area ie., 18" stone walls at one end that isn't practical to insulate inside as we would not wish to detract from the character).

Thanks again for your help.