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 Post subject: heat in the winter
PostPosted: Apr 24th, '13, 10:24 
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i have been searching the web all day searching for heat alternatives for my greenhouse in the winter at night will a solar panel charge batterys enough throughout the day to run a heater at night. I know its spring but im planning ahead


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 Post subject: Re: heat in the winter
PostPosted: Apr 24th, '13, 10:46 
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Short answer- No.

Solar panels are only about 15% efficient for a decent quality panel, so even if you had 1 square metre of panel, you could only produce 150W at best, when the sun was face-on to the panel. Then if you are storing that power in Lead-acid batteries, their charging efficiency is only about 85%, so you are down to 127W, then if you are converting to 110VAC to run your heater, theres another efficiency loss, with a small inverter lucky to be 80% efficient. So now you are down to 100W, for the number of hours that you had full sun during the day. If you are talking about winter in ID, then that might only average 2 hours/day.
So- a 100W heater for 2 hours per night- its going to make bugger all difference to the temperature in your greenhouse, unless you have a very large array of panels.

Evacuated tubes to heat the water are vastly more efficient, I'll be using 24 of them for heating my fish tank in winter.

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 Post subject: Re: heat in the winter
PostPosted: Apr 24th, '13, 11:07 
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oops i was refering to heating the inside of the greenhouse. FT water i have already solved water heating issues.


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 Post subject: Re: heat in the winter
PostPosted: Apr 24th, '13, 12:41 
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You can heat the air space by heating the water- it will radiate and conduct heat into cooler areas, but the amount of energy available from PV panels makes it an expensive and inefficient way to do it. If you dont want to heat the FT water any more- use hydronic radiators with the evacuated tubes, and fans to circulate the air. If the greenhouse has no or minimal insulation, it's going to be expensive to heat to a comfortable temperature in an ID winter night via any means.
A large mass of hot water is about the best way to store heat, due to the high specific heat capacity of water, so putting that, probably at least a ton of water (although I dont know what air volume you are trying to heat), in the greenhouse and using direct solar energy to heat it would be a good start.

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 Post subject: Re: heat in the winter
PostPosted: May 14th, '13, 03:48 
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Hi!

this topic is most interest to me, as I want to run my AP system year round. Let me explain my scenario and feedback on heating would be GREATLY appreciated

  • I live suburbs of Vancouver, BC, Canada. In winter, we have temperatures in the range of -7 to +7 C, with very occasional -13 C
  • In y area, we get very little sun in winter. Our climate is very similar to Seattle, which is 2.5 hrs drive away. In the valley, where I am, we get almost never snow, but constant rain and cloud cover
  • I am looking at getting LED lights to supplement the plants with light - I mention LED because it will not produce enough heat to account in the overall heating strategy
  • Greenhouse size is around ~18' x 9' and varies in height from 9' to 7'
  • three sides of the greenhouse will be insulated with standard 2x4 and type R14 insulation and thin plywood with vapor barrier
  • Ceiling and front highest wall is made out of greenhouse type woven poly, which lets 100% light in and is durable. These polys will be doubled up, with space between them of about an inch, inch and a half. Then a blower will be installed which will have a tube going in each 'section' of the wall/roof (between rafters) to inflate the space to provide a cushion and greater insulation (University of Manitoba has done research on this, and they do such tripple layer inflated walls / roofs and had amazing results)
  • I will be digging the entire area of the greenhouse to a depth of 1 meter (depth of the IBCs). The layout is a simple walkway in the middle, with GB on the left and right. Beds will be made out of wooden structure, to a depth of about 30cm, using pond liner (I calculated this to be even cheaper option than using IBCs for GB, and you get to make them to your own size). Under one row of GBs, the fish tanks will be in the ground.
  • The fish tanks will be insulated; however I am starting to think I should just insulate instead the perimeter of the dugout hole of the greenhouse only. And then leave the piping and tanks 'exposed' so that the warm water from them would also heat up the greenhouse
  • If my calculations are right, I will have about 4000L of FT (although not all the tanks may hold fish at any time; I might devote one for 'sick bay', one for fingerlings, and other two for full grown fish. Each tank could be isolated from the rest (the afore mentioned sick bay) or connected with the rest with just a valve
  • As for the GB, I might be somewhere in the range of 2500 to 3000L.


Questions:
  • Given my description, what would be the best way to heat
  • I am considering heating the water with a hot water tank style 'elements' - or perhaps to simplify things, just get a used hot water tank and connect it to the rest of the system, with obviously lowered temp to not fry the fish (I wonder if there would be concerns over the materials used in a hot water tank)
  • Would there be any need to heat the greenhouse at all or would the evaporation from the water tanks do the job. I understand the air can be cooler than the water and plants will still thrive; but there is obviously a threshold here. I am aiming at growing summer loving plants such as tomatoes, peppers, cucumbers...
  • How did you adapt your hot water system? Especially with the evacuated tubes? I am unsure if you'd get enough heat from those tubes to last you the night? I thought this link was interesting to this topic: http://www.skylineenergy.com.au/why_sol ... t_work.php


Thanks for your time and anyone chipping in to educate me!


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 Post subject: Re: heat in the winter
PostPosted: May 14th, '13, 12:34 
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Insulation is good, so you are not wasting too much of the heat you are adding.
If you don't get much sun in winter (The couple of weeks I was in Vancouver/BC in late November 99 were certainly gloomy with lots of rain and snow- I don't remember seeing the sun at all!), then evacuated tubes are probably not the best way to go, but here in my situation with some winter sun, they are way ahead of heat pumps. Heat pumps are way better than resistive element heaters, which would be much more expensive to run, for a given amount of heat, so a heat pump may be the best heating option for you. Ground source heat pumps will be much more efficient than air source in very cold condtions, but cost more up front.

I think just heating the water may be sufficient, as it will release a fair amount of heat to the air in the greenhouse, and the double skin should reduce losses. It may get a bit foggy in there at times, in particularly cold weather, with a body of warm water evaporating lots of moisture, and there may be a fair amount of condensation on the coldest parts of the structure.

NiKDo wrote:
[*] How did you adapt your hot water system? Especially with the evacuated tubes? I am unsure if you'd get enough heat from those tubes to last you the night? I thought this link was interesting to this topic: http://www.skylineenergy.com.au/why_sol ... t_work.php[/list]


They don't appear to know the difference between kW and kWh at that site, so I woudnt be paying too much attention to it.

As I mentioned previously, water is very effective at storing heat- and its a matter of being able to store heat when the sun is available and releasing it when the AP water needs heating. In my system thread I've written a bit about how I plan to do that, using the evacuated tubes and the phase change of wax to store a bit more heat than water alone can. Evacuated tubes work much more effectively in cloudy and cold conditions than flat plate collectors, although they have improved a bit in recent years.

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 Post subject: Re: heat in the winter
PostPosted: May 14th, '13, 23:02 
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thank you for you insight and suggestions.

I believe that I will be building my system with making some important decisions upfront - those which I cannot modify later on (or modify with significant effort), and the rest I will experiment with and figure out what works best.

As such, I know that I will definitely insulate the perimeter of the dugout hole. I will simply use plastic as a barrier and straw bale hay, cut with a chainsaw to about 6". That should be good.

Everything will be modular as much as possible, so things can be changed a bit if necessary.

I have few more questions if you could answer please:

- should I just insulate the perimeter, or should I insulate the IBCs, pipes and beds?
- Or should I expressly NOT insulate then, wanting them to release some of the heat to the surrounding area? Or perhaps insulate them, so the heat would be retained better and moisture build up in the greenhouse would be minimized, and also use the heat pump to warm up the air (if I were to use the heat pump anyways)
- should I use a hot water tank type element to heat the water? Or should I somehow try to fashion the heat pump to heat the water?


I wish I could find a decent heat pump that would not break the bank that I could take the pipes from and run them through the water to heat up the water directly, as we all know air to water transfer is inefficient.

Thanks!


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 Post subject: Re: heat in the winter
PostPosted: May 15th, '13, 05:54 
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NiKDo, Strawbale biscuits are excellent insulation, but you will need to make them waterproof if you want them to last- they will rot away in a damp conditions/soil.

NiKDo wrote:
should I just insulate the perimeter, or should I insulate the IBCs, pipes and beds?


If you want to be heating the air as well as the water, then you may as well leave everything inside uninsulated.

Use a hot water heat pump, not one for heating air (ie reverse cycle air conditioner), heat the water via a heat exchanger, rather than using the water directly, and perhaps use some hydronics radiators to heat the air as well when it is very cold if needed, if the heat from the FT, GB, pipes etc isn't enough. Perhaps the heat from the water in the GBs will be enough to protect the plants and you dont need to worry about heating the whole volume, which will take a LOT of energy when it is below zero outside.

Quote:
- should I use a hot water tank type element to heat the water? Or should I somehow try to fashion the heat pump to heat the water?


That is going to cost you more to run than a heat pump, but initial cost will be much lower- so you have to decide, is it worth the investment... how long term a project will it be?

The heat pump hot water will typically be around 65C, so you need to be careful not to generate hot spots in the FT- maybe run a pipe around the outside of the tank, like I have done (see pic in my system thread), but inside the insulation. You could also run a pipe under the gravel/clay in the grow bed to add heat directly to the GB. that should protect the plants reasonably well, and deliver warmed water to the FT.
It is going to take some experimentation before you add fish through, so you can gain an understanding of how the heating system performs with varying water circulation flow rates, HP water temperature, etc.

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 Post subject: Re: heat in the winter
PostPosted: May 15th, '13, 06:25 
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Gunagulla wrote:
NiKDo, Strawbale biscuits are excellent insulation, but you will need to make them waterproof if you want them to last- they will rot away in a damp conditions/soil.


Totally agree - i will protect the hay to avoid the rot for sure, especially at the perimeter wall which will then be blocked by the FT and would be hard to change after.

Gunagulla wrote:
If you want to be heating the air as well as the water, then you may as well leave everything inside uninsulated.


That is what I was kind of thinking too. Insulate the perimeter wall, and then put the FT tanks in. If, I decide to change my mind later, I could easily insulate the tanks afterwards

Gunagulla wrote:
Use a hot water heat pump, not one for heating air (ie reverse cycle air conditioner), heat the water via a heat exchanger, rather than using the water directly, and perhaps use some hydronics radiators to heat the air as well when it is very cold if needed, if the heat from the FT, GB, pipes etc isn't enough. Perhaps the heat from the water in the GBs will be enough to protect the plants and you dont need to worry about heating the whole volume, which will take a LOT of energy when it is below zero outside.


Now this is the part that is very interesting to me and I know least about. I am totally on the same page with you - use hydronics and radiators and heat exchanger. The part I don't know is where to obtain or build such devices. I am having real trouble finding them - I am sure I am not looking at the right places. Even if I got some companies local to another country - that is ok, it would at least give me idea of what it costs, the makes, models, etc and I could then try to find it locally.

Or is it somehow home made from spare parts? You mention reverse cycle air conditioner - do you mean this literally? To use and old air conditioner and fashion it into a heat exchanger? If so, any pointers on the web where to look at some how tos? I am quite handy, but don;t have experience in this field, so some tutorials in this respect would go a long way to put me on the right path.


Gunagulla wrote:
That is going to cost you more to run than a heat pump, but initial cost will be much lower- so you have to decide, is it worth the investment... how long term a project will it be?


I won't say money is not an object; however this project is very important to me. Long term goals are to make this an educational project, get kids involved, learn about food security, learn about the ins and outs about AP to do it later at a much bigger scale at an eco village. Also I would be writing an open source software for automation of AP systems. So yeah, I'm in it for the long haul, not afraid of work or failures and so I will make the necessary investments that need to be made.


Gunagulla wrote:
The heat pump hot water will typically be around 65C, so you need to be careful not to generate hot spots in the FT- maybe run a pipe around the outside of the tank, like I have done (see pic in my system thread), but inside the insulation. You could also run a pipe under the gravel/clay in the grow bed to add heat directly to the GB. that should protect the plants reasonably well, and deliver warmed water to the FT.
It is going to take some experimentation before you add fish through, so you can gain an understanding of how the heating system performs with varying water circulation flow rates, HP water temperature, etc.


I agree it will take experimentation. I am thinking I will have it ready end of summer here in North America, and coming fall and winter, I will run many tests - dry runs, no fish or plants. Once things are all figured out and wrinkles ironed out, then I would cycle the system and get things going

Thanks for your continued help, it is making a huge difference. As many others I am perusing the forums and learning a lot, but sometimes it is a bit hard getting the exact info you seek.

Cheers!


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 Post subject: Re: heat in the winter
PostPosted: May 15th, '13, 07:04 
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NiKDo wrote:
Totally agree - i will protect the hay to avoid the rot for sure, especially at the perimeter wall which will then be blocked by the FT and would be hard to change after.


Dont use hay! ;) Higher Nitrogen content will mean it will decay, use straw- high C low N.

Heat pump hot water systems, I would think, should be very common in your part of the world. Just look up heat pump hot water systems online, also heat pump hydronics systems. Both are easily available here in Australia.

For the "heat exchanger" you dont need anything more than a pipe in water- the purpose is to keep your AP water separate from the hot water- you only want a thermal exchange, but not mix the water. A pipe buried in the GB - 2 or 3 loops, probably paralleled loops in each separate grow bed (assuming they are reasonable size) then back to the storage tank. Use something like Pex-Al-Pex pipe, so you dont have bare copper or Aluminium exposed to the water, the fish dont like it.

I mentioned reverse cycle air conditioner because that's basically what a heat pump is, in that case for heating air. You want one that heats water. It would be a fairly major undertaking to try and DIY a water heat pump from an air conditioner, so best to buy one suited to the task, IMO.

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 Post subject: Re: heat in the winter
PostPosted: May 16th, '13, 03:07 
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Gunagulla wrote:
Dont use hay! ;) Higher Nitrogen content will mean it will decay, use straw- high C low N.


Goot to know; I'll keep that in mind

Gunagulla wrote:
Heat pump hot water systems, I would think, should be very common in your part of the world. Just look up heat pump hot water systems online, also heat pump hydronics systems. Both are easily available here in Australia.


You'd be surprised how backwards north america can be. Our politicians still think here it's the land of infinite resources we can keep exploiting - just look at the tar sands of Alberta!

I'll have to do more research on where to get one

Gunagulla wrote:
For the "heat exchanger" you dont need anything more than a pipe in water- the purpose is to keep your AP water separate from the hot water- you only want a thermal exchange, but not mix the water. A pipe buried in the GB - 2 or 3 loops, probably paralleled loops in each separate grow bed (assuming they are reasonable size) then back to the storage tank. Use something like Pex-Al-Pex pipe, so you dont have bare copper or Aluminium exposed to the water, the fish dont like it.


yes, I will have the water circulation separate. That makes sense for a lot of reasons. What I am wondering though, is why you suggest to heat up the GB, when heating up a FT would be far easier to plumb?


Also, I was musing a heat pump hot water exchanger. I came across a residential hot water tank heated by a heat pump. this may be the best option - price-wise as well. The caveat is where to place it. I believe these systems use 240V and N. America is 110V. My greenhouse is about 20m from the house in a small suburban area. I don't believe we are allowed to run current to the greenhouse, unless it is an extension just plugged into an outlet.

So, I was thinking perhaps to replace my current hot water tank at home (electric) with this new heat pump one. Furthermore, I would reinforce my attic and place it there. That should be good, because the attic is often hot or at least warm - the heat pump would definitely be more efficient there then outside even in winter.

Then I would run an insulated pipe from the attic, down to the ground floor (inside the house) and then protrude it to the outside and bury it for the length to reach the greenhouse.

Inside the greenhouse, I could then make a loop, or perhaps plumb it to a radiator to increase surface area, to heat the greenhouse. As well, another pipe coming from the same input would then heat the FT.

I have to read up more on how to plumb it though. since this would be a combined tank for home use and the AP; I probably would have to make a branch coming out of the tank to the AP and put some circulating pump on that.

Tell me my idea is crazy enough to work! :)

Cheers


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 Post subject: Re: heat in the winter
PostPosted: May 16th, '13, 07:49 
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NiKDo wrote:
I am wondering though, is why you suggest to heat up the GB, when heating up a FT would be far easier to plumb?


I have suggested both ;) Heating the GBs directly will protect the plants a bit more from frost.

Surely someone makes 110V heat pump water systems in the US? :? The voltage is just for a compressor and fan motor, I'm pretty sure they exist over there :lol:

A heat pump will only use ~one third to one half the electricity of a reisitive element water heater (depends on ambient temps), so you can save a bit on your energy bill if you replace your existing HWS.

I don't know your house structure, but you probably dont want a HP next to your bedroom for example, as the compressor might be a bit noisy at night. In Australia most people put them outside. I think the new CO2 refrigerant ones operate quite well in low temperatures.
Not wanting to promote any particular brand, but as an example, see:
http://solarhydronics.com.au/co2-heat-pumps/

I would probably concentrate on heating the water, and mostly convective and conductive heat from that will heat the air, probably with less losses than using the hot water to heat the air directly.

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 Post subject: Re: heat in the winter
PostPosted: May 16th, '13, 19:34 
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I've been following this thread with interest.

NiKDo I plan to build a greenhouse very similar to you it seems, with one walkway down the middle to maximise space used, and digging in 1m to create a pit greenhouse.

If you have access to firewood have you considered heating your greenhouse at night with a rocket mass heater with a big hopper so you could leave it unattended?

Or if you have access to waste vegie oil, a waste oil heater? http://journeytoforever.org/biofuel_lib ... h/me7.html

From what I've read, the waste oil heater would require the least maintenance and least amount of fuel. Each night you'd basically just need to light it, adjust the flowrate and the oil is gravity fed in from a storage tank.

With both the above, you could attach a heat exchanger to the stoves to heat both your fish tank water and the airspace inside the greenhouse.

I'm thinking of using a hot water pump controlled by a thermostat to pump water through the heat exchanger and back into the fishtank. Only thing I haven't quite worked out is how to start/stop it safely, or regulate it.. ie when the thermostat is off, how do I stop the water left in the heat exchanger from boiling dry etc?


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 Post subject: Re: heat in the winter
PostPosted: May 17th, '13, 02:00 
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Gunagulla: Again, thanks for taking time to reply. Past few days I have been checking out heat pump water tanks. Yes, there are few brands. Most sell in USA; very few in Canada and you have to call for a quote. Many are above $2K Canadian, which is really pricey (regular hot water tank will set you $400 or less). Yet I would be willing to bite the bullet.

I will obviously have to investigate more. If that hot water tank could be used to also heat my house, well then it is an even better investment. But I don't know if that would be sufficient for both systems - home and AP. As for putting it in the roof - well it is insulated and the heat pumps are very quiet, so if I put it on silent blocks like engines are, it won't even vibrate.

Obviously many questions remain, such as if that hot water tank can be put down on its side and not standing up, as there might not be enough height for it (especially after I build a reinforced floor for it), how to plumb it with a recirculating pump to the AP, and on and on and on. But all with due time

I could put it in the garage, but that is quite an exception here in Canada, because normally that is not done, for your hot water tank would be cooled needlessly and in many areas pipes would freeze. I am lucky that in Vancouver, due to the influence of the ocean, we have mild climate


jono81: I am happy to see others are taking interest in this topic and chipping in on the conversation.

As I mentioned in an earlier post on this thread, I as well will be digging to the dept of the IBCs and I too will have a walk path in the middle and grow beds on each side.

I have considered the rocket stove. Perhaps I should again. Who would not like a free heating, right? It would alleviate the huge cost of buying that heat pump hot water tank.

I initially wrote that idea off, because I am going through a divorce and although I am keeping the house, I won't be keeping the car. Since I live in suburbs and pretty centrally, I decided to forgo the car completely and will instead get a good bike. That being said, I wondered how difficult it would be for me to get a source of used vegetable oil. Perhaps I should have a call around and find out. After all I do have a kids buggy that you attach to a bike and I could get the veg oil that way - probably get it once a week or something.

If I were to go that route, I think that I would likely affix a decent sized tank on the outside, at a decent height and top it off. That way this sucker could keep running for many days.

I would need to find out how to make this safe; for I am sure if the damn place burned down, my insurance would cover nada. I don't even know if this kind of setup is allowed - probably not. They're really backwards here in many places in North America when it comes to alternatives and forward looking sustainable practices.

Also, just as you said, how would one control the flow to regulate the temperature. As well, I wonder if a system could be fashioned that would actually be able to start this and stop it. I am doing AP with the goal of automating things with software that I will write and inexpensive hardware and sensors and servo motors. I think opening a valve and closing it for the oil drip would be easy. I wonder how hard would it be to have something to automatically light it up once the temp drops and you want it to get going again.

In any case, fascinating topic and I will look in that direction as well. If this were to work out, man, this would be a bomb. I could make the greenhouse a freaking sauna, and if I were to add LED grow lights, then food and fish production would be guaranteed year round, and this, is my ultimate dream and goal.

Keep me posted on your progress and I will do the same.

Cheers from Canada


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 Post subject: Re: heat in the winter
PostPosted: May 17th, '13, 08:17 
Be aware.... most household hot water systems are designed to produce water at 60C+... far to hot to add to a fish tank....

They achieve those temps by copper elements/heat exchangers..... also bad for fish....

So you need to have a separate loop for any "hot water" system... and a heat exchanger that's not toxic to fish....

And that means that most are pretty inefficient....

Then there's the reality... that most of the heat is lost... during the night... and from the tank surface... or by draw down of cold air through the grow beds....

I've run a purpose built evac tube system previously... and yep, on a good sunny day... getting heat into the tank was no problem....

Keeping it in during the night was a big problem though....

Phase change substances.... are worthy of investigation... (I never got around to it, but had it sussed in my head)....

But again.... you need the heat during the night... and most phase change materials give up their latent heat pretty quickly... :wink:

You can see my thread o the forum somewhere.... called "aquaheat" from memory...


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