navitron
 
Renewable Energy and Sustainability Forum
Welcome, Guest. Please login or register.

Login with username, password and session length
News: Anyone wishing to register as a new member on the forum is strongly recommended to use a "proper" email address. Following continuous spam/hack attempts on the forum, "disposable" email addresses like Gmail, Yahoo and Hotmail tend to be viewed with suspicion, and the application rejected if there is any doubt whatsoever
 
Recent Articles: Navitron Partners With Solax to Help Create A More Sustainable Future | Navitron Calls for Increased Carbon Footprint Reduction In Light of Earth Overshoot Day | A plea from The David School - Issue 18
   Home   Help Search Login Register  
Pages: [1] 2   Go Down
  Print  
Author Topic: Heat Store under south facing conservatory  (Read 3349 times)
Phil.Chaddah-Duke
Newbie
*
Offline Offline

Posts: 10


« on: August 03, 2020, 11:14:47 AM »

Hi all,

Looking for some advice please, I am currently building a 8m long south facing conservatory (unheated) in Glos, UK on the side of our house, during construction I allowed for a 7.5 x 0.7 x 0.7m insulated void under the floor with the aim of creating some kind of heat store to maintain a more even temperature.  I was originally thinking of using stone and blowing warm air from the roof of the conservatory through it during the day but obviously water would retain much more heat.

Questions:
-  Is that space (4m3) enough amount of storage to make a difference?
-  If I used water, would blowing warm air through a metal pipe through the water transfer heat?
-  If I used water, could I use some kind of small air source heat pump run off a PV panel to warm the water directly or do they require a significant amount of elec?

Thanks for any advice.
Phil

  
Logged
Countrypaul
Hero Member
*****
Offline Offline

Posts: 1907


« Reply #1 on: August 03, 2020, 11:37:59 AM »

The COP of an ASHP varies with the output temperature of the water you are heating up. In general if you are looking for quite low temperature water say 30C and the air temeprature is quite high 20C+ you should get a very good COP of 4 or higher. That means for every Watt of electrical energy you put into the ASHP you should get 4Watts out.  In winter you might find that the COP is much lower and may struggle to achieve 3.  If you plan on putting in a water store of 4m3 that could certainly store a significant amount of energy, 4MJ/K per m3 (1MJ = 1,000,000 Joules or WattSeconds, K = Kelvin equivalent to degrees Celcius in this case)  If you had 250Watts electricity from you panel + storage inverter/battery that could translate into 1KW of heat, so about a 1K rise in temperature of a 4M3 water store  per hour.

No idea how much heat you want in your conservatory so the above is an example, and finding a small ASHP might be a challenge (let us know if you find one). The reason I have put a battery in the example is that an ASHP works best if run for a continuous period and not on /off all the time , so a battery would allow you to store some charge and ensure the ASHP ran for longer periods that just a couple of minutes. You will also need to check on the volume of you conservatory and balance that with the size of your ASHP as you wouldn't want the ASHP to chill the conservatory from 30C to 0C in 2 minutes!

Bear in mind that PV would only be generating significant electricity in spring/summer/autumn and that in winter (depending on location) you are likely to get diddly squat from it.

4m3 woud certainly be enough water to stabilise a large conservatory to some degree, but don't expect it to provide a warm conservatory in the middle of a cold spell during winter.

Blowing air through say an old car radiator to warm the water instead of an ASHP would probably be much more efficient that just using a metal pipe, and could also be used to push the warm water though to warm the air when the air temperature drops suficiently low.
Logged
Phil.Chaddah-Duke
Newbie
*
Offline Offline

Posts: 10


« Reply #2 on: August 03, 2020, 01:02:16 PM »

Thanks Paul, I must admit the idea of sinking some kind of heat sink into the tank worries me long term with corrosion, it will be directly under the floor so not easy to change it later.  Hence would prefer to pump water out and heat it externally somehow, good to know that heat pumps are better working continuously.  Maybe a timer switch  along with a temperature sensor so it runs for a specific amount of time if the air temp is above a certain level but finding a small enough model does seem challenging, quick look on-line they all seem pretty big units.  I am guessing that it could be alot smaller (if they exist) given we would be pulling warm air rather than cold outside air.   
Logged
Countrypaul
Hero Member
*****
Offline Offline

Posts: 1907


« Reply #3 on: August 03, 2020, 02:45:31 PM »

The heat capacity of air is around 900J/M3K at 0C, this will drop as the temperature increases, so around 800J/M3K at 30C.

If you are cooling air as with an ASHP then the humidity can contribute a significant amount of heat (the ASHP will produce condensation that needs draining away).

If your conservatory is 75m3 and you drop the temperature from 30C to 20C that would give you 75 x 10 x 800J or 6MJ.

In theory that would give you 8MJ of heat in the water (assuming COP of 4), so 2C per hour increase in temperature for a 4m3 store.

You might also want to look at a thermal solar solution as that might be simpler and cheaper to provide an amount of hot water.

If the tank si not easily accesable, I would certainly keep the heat exchanger outside the tank and basically have the water in an almost closed system, with inhibitor to minimise corrosion and possibly some suitable antifreeze (expensive), or else an external heater to be used only if needed (ie. water down to 0C), with the water raining back into the tank so all pipes, heat exchanger etc. are empty if frost does take hold if you use an ASHP this may require a separate loop with antifreeze in and say a FPHE.

Whether you could use something like this I'm not sure (just the first small ASHP I found) https://www.swiminn.com/swimming/gre-mini-heat-pump-up-to-30-m3/137584168/p?utm_source=google_products&utm_medium=merchant&id_producte=10819070&country=uk
You should also try ringing Navitron and asking them as they often seem to have things that are not lists on the website.
« Last Edit: August 03, 2020, 02:51:15 PM by Countrypaul » Logged
Phil.Chaddah-Duke
Newbie
*
Offline Offline

Posts: 10


« Reply #4 on: August 03, 2020, 03:47:33 PM »

oh yes that looks good size.  We have already used up available space with solar for the main house so need to make use of warm air in the sunspace rather than more panels.  The conservatory will be 40m3, the objective is to create a space where plants will grow year round with no danger of frost damage.  Sorry few more thoughts:
- Wondering about how to release the heat, if I insulated the top of the tank with some slots, would heat simply rise out or would I need to a pump to extract the heat?
- The top of the tank is beam and block which I could cast a concrete floor straight onto with no insulation but I assume with no insulation the heat would escape to quickly as soon as the inside air cools down?
Logged
Countrypaul
Hero Member
*****
Offline Offline

Posts: 1907


« Reply #5 on: August 03, 2020, 05:02:15 PM »

You say the top of the tank is Beam and Block - is the whole conservatory floor? If so what comosition are you planning on top of the B&B - DPM, Insulation (100mm PIR or what), screed (S&C or flowing)? Could you put UFH pipes in place - that might give you plenty of option for the future as well?

I suspect in winter you will need to put some additional heat into the conservatory as the amount of sunlight will be insufficient to keep the place warm when it is dark winter days. Either UFH or radiators might be options you could connect to another heat source for winter - especially if you want to the temperature up at that time so plants still grow.

Logged
ceisra
Full Member
***
Offline Offline

Posts: 122



« Reply #6 on: August 04, 2020, 07:27:36 AM »

This is very similar to an episode in the original series of "It's Not Easy Being Green"

A  little bit of searching gives  https://en.wikipedia.org/wiki/It%27s_Not_Easy_Being_Green

Series 1 episode 2   
A greenhouse is erected with a unique heatsink designed by Dick and made from recycled bottle glass to keep it warm and the family acquire two pigs, ominously named "Christmas" and "New Year". 
 
I don't know if the heat sink was improved or there is better material these days but the episode was interesting.

The best method of background heat in a conservatory in winter is a storage heater and there is loads of info if you use the search option on this forum.

Roger

   

Logged

16 X 240W Panasonic panels with a 3.6 ABB ( PowerOne ) inverter
http://pvoutput.org/list.jsp?id=40128&sid=36661
Phil.Chaddah-Duke
Newbie
*
Offline Offline

Posts: 10


« Reply #7 on: August 04, 2020, 10:01:32 AM »

Yes Paul, the tank is whole length of the space but only half the width as there were services running along the other half, yes I was thinking DPM and screed so could put in UFH pipes, although bit of a slippery slope as definitely don't want to start heating the space using fossil fuel sources but I guess electric (as we use renewable supplier would be ok for the really cold times). I assume from your comments having simple slots to allow heat to rise wouldn't be sufficient then, some kind of active system would be required to draw heat out?  Are you thinking I could pump the water from under the floor through the UFH pipes?   

Roger, thanks for link, actually that's the episode that inspired me originally to dig out the space during construction, it was very basic and small amount of thermal mass in his Greenhouse but according to Dick was very effective in extending the growing season so figured with even more space could get even better results  Smiley
Logged
Countrypaul
Hero Member
*****
Offline Offline

Posts: 1907


« Reply #8 on: August 04, 2020, 10:36:43 AM »

Yes, I was assuming you would pump the water from the tank either though a FPHE and then circulate through the UFH, or directly. If directly, then would would not be able to allow drain back of the UFH pipes so what would you do if there is a significant very cold spell? Once the heat in the tank is used up you and assuming you have not put antifreeze into the tank, you would have to introduce some heat (immersion heater for example) just to prevent the UFH pipes from freezing. Using a FPHE and a "closed" circuit for the UFH (and ASHP?) with antifreeze might be an option.
Do you have a PV diverter at present, if not you could consider fitting one to heat the tank (again I would not put it directly in the difficult to access tank, but inline with a pump).

My view on having simple slots in the floor is that they might well work short term, but longer term I suspect they will get blocked and be difficult to clean, what happens when a floor covering is considered (you say "we have ...") so it may not be entirely your choice  Grin

A more complicated option might be to see if the ASHP can be ducted, so in summer it can be used with the hot air inside the conservatory to heat the tank, but in autumn/winter/early spring it could be used with external air. Obviously the COP when using external air will be nowhere near as good, but then you would only use it whe it looked likely that you would need direct heating to prevent internal frost - just an idea.
Logged
Phil.Chaddah-Duke
Newbie
*
Offline Offline

Posts: 10


« Reply #9 on: August 04, 2020, 12:04:49 PM »

I was imagining kind of vertical vents up the back wall bringing them up out horizontal above the level of the floor covering, if this would work would be much simpler, I guess I could install these along with the piping into the tank and see how we get on, can always add the FPHE later on if needed.  Good idea about the ASHP and venting from inside or outside, that would be perfect solution, avoiding another heat source.
Logged
Countrypaul
Hero Member
*****
Offline Offline

Posts: 1907


« Reply #10 on: August 04, 2020, 12:42:42 PM »

Would you be looking for an airflow through these slots, in which case where would the air enter and leave? If both are at similar heights you may need some sort of forced air curculation - eg. fan system controlled by thermostat etc. You probably don't want external air (very cold) drawn in during winter when you most need the heat. I had in mind slots like you see with warm air heated housing by more passive - clearly your idea makes much more sense.
Logged
Phil.Chaddah-Duke
Newbie
*
Offline Offline

Posts: 10


« Reply #11 on: August 04, 2020, 12:59:13 PM »

oh good point, I was thinking the hot air would simply rise but of cause it will have to flow from somewhere, maybe a duct that passed from low down point across the top of the tank with slots and existed higher up on the other side, the cooler air would be lower down so would the air flow in low down and out higher up?   

Also one other point, more building question but do you think a heavy duty pond liner would be sufficient to line the tank, I assume that in a non-UV environment like that it would last indefinitely?

Getting excited now about building it Smiley
Logged
knighty
Hero Member
*****
Offline Offline

Posts: 2888


« Reply #12 on: August 04, 2020, 01:32:12 PM »

if you went with a water tank, you could add UFH for overnight heat from the water

and then add some sort of heat collector - have it on the inisde and make a featuer out of it?

I'm trying to think of a way to make some radiators painted black look good, or evacuated tubes on the wall

you'd need to cover them in the summer... but a blind would work well for that


a very low power pump would work - if you want totally renewable I'm pretty sure there's some solar/battery/pump setups avalible off the shelf
Logged
Phil.Chaddah-Duke
Newbie
*
Offline Offline

Posts: 10


« Reply #13 on: August 04, 2020, 01:59:34 PM »

Yes, that would be an option but I am trying to keep it simple, hence the hope that convection would work, I am not trying to keep the space cozy warm to use on winter evenings for example, its more about keeping it a safe temperature to grow lots of cool plants.  Our house has already got so much tech with Thermal stores, UFH, PV, Solar Thermal, the plant room looks like the titanic engine room Grin 
Logged
brackwell
Hero Member
*****
Offline Offline

Posts: 3579


« Reply #14 on: August 04, 2020, 09:07:29 PM »

What kind of temps are you looking for summer,winter,day,night. Is it 24/7/365 ? Need to decide the objective first as there are huge variations.
Logged
Pages: [1] 2   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.20 | SMF © 2013, Simple Machines
SMFAds for Free Forums
Simple Audio Video Embedder
Valid XHTML 1.0! Valid CSS!