# How do greenhouse growers keep heating costs down



## blondie (Apr 16, 2017)

Hi 

So I had a wonder full letter from the electric company saying our electric bill coil be going up buy £1000 increase, over this year. 

Well before this I was planing on renovanting the greenhouse and way and try in tomake the greenhouse more energy efficient and cheep all round. Now even more so. The main catalyst was to give the greenhouse a deep clean, after finding the main insulation was knackered. 

So now I am going to be spending a few hundred pounds on the greenhouse. I am using something called airtec as the first layer which is a, silver double bubble insulation to keep heart in and in summer keep what out. ThatI shall have around the sides upto the high of the benching, but then on the one side it will go up to hieght of the roof and on the end of the greenhouse will be completely covered in it.
The second layer will b 250mm celotex insulation boarding they will be the same height, as the benching all the way around. Then the third layer will be UV treated bubble wrap that will cover all the side and not get taken down. I am also hoping the insulation with it being silver will reflect more light in the winter months. 
I will still be bubble wrapping the roof by that gets removed each year so I can but up a layer of netting. 

I shall also be building all new benching in the greenhouse as the only bench is ready to fall apart I think in some places, it's only the rust holding it together.

So how are other people heat in there greenhouses and keep the costs down and becoming as energy efficient as possible.


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## NYEric (Apr 16, 2017)

Ask Dot, besides insulation there are heat sinks and other methods. Good luck.


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## JAB (Apr 16, 2017)

One of the sole reasons businesses fail and personal collections can no longer be maintained. Insulation. Smart install. Really all depends on the initial setup. After market upgrades are tough to maintain efficiency.


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## tomkalina (Apr 16, 2017)

Start by replacing all of your glazing with 8 ml. twin-wall polycarbonate.


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## blondie (Apr 17, 2017)

tomkalina said:


> Start by replacing all of your glazing with 8 ml. twin-wall polycarbonate.



That shall be ny next step but that is a costly task so need to save up for that.


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## Ray (Apr 17, 2017)

Believe me, it'll be better if you "bite the bullet" and do it sooner, if you can. With so-so insulation, you'll be paying considerably more to heat the thing, making it a longer-term savings effort. Put the better cover on immediately, and the energy cost savings will pay it off much sooner.

The thicker, and with more walls you can get, the better.


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## blondie (Apr 17, 2017)

Afternoon 

Just doing some quick calcuations and if I went down the 8mm twin wall pollycarb im lookin at very roughtly £1947.44 to do my greenhouse, plus indont know if ill be able to clip that size into my glazing bars.

I could buy three greenhouse that size lol.

Most of the pollycarb sold in the UK for a greenhouse is 6mm. 

This options would have to be a long haul as it is way out my budget this year in all honestly, or it might have to be done in stages each year.

Rome wasnt built in a day as they say.


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## abax (Apr 18, 2017)

A cheaper way than polycarb is dead air spaces between
layers of 6mm greenhouse plastic and fiberglass. I also
have a heavily insulated knee wall. Other than that, I just
pay the damn bill and roll my eyes every month.


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## blondie (Apr 19, 2017)

Yes the hole reason this has come up is the orginal insulation has been there for 10yrs now, and is very tasty and dissintergrating so it time to change. 

Plus the greenhouse has not really had a full clean in years, well since I turned it over to the orchids.

I have been able to bring the price down year on year, but this coast increase is over allon electric price so if I can minminimise I want to.

Also I though as I am doing the hole greenhouse over hall benching and all, I would be stupid not to ask the question as to what others do.

My over all goal is to be the base area under then benching as insulated as possible. Then when I have the money to slowly move towards the pollycarb route.


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## Bjorn (Apr 22, 2017)

Living in a moderately cold area, I have chosen to insulate with heavily insulated knee-wall as Angela, plus two or three layers of 10mm double walled poly. This sounds quite excessive but it pays off. Now the heat from the lights is enough to keep up the temperature. And btw. A thermostat shuts off the light when temp is high enough.
One very important thing to do if you have an aluminium structure, is to break the heat transfer through the ribs. This can account for more than 50% of your total heatloss. I did that by putting a layer of poly outside the entirely greenhouse covering all metal and everything that conducts heat. Also the vents are blocked, cooling in summer is done by fans blowing in fresh air if necessarily. The latter is unfortunately not always the case in my climate though. Even in summer. My point is that you will have to adopt to your lical climate with these things.
Good luck


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## Ray (Apr 22, 2017)

We need to be clear on this one (no pun intended): in the industry, "poly" typically refers to polyethylene film, typically 6 mil thickness, UV protected, and often with infrared-trapping-, and/or drip-preventing coatings. Two layers are inflated with a small fan, and that becomes an effective insulating layer. Something you might consider, Blondie.

The multi wall, rigid stuff - polycarbonate - is referred-to as "polycarb" or just "PC."


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## blondie (Apr 22, 2017)

The Pollycarb is a root I will be going down at the moment it is just unaffordable at the moment. 

I have been play with ideas and you guy's have give me some extra ideas I shall what I'm playing as I will be increasing insulation and keeping the price down. The coldest I do at in normal winter is -7C. Overall the electric bill is going up as a hole but I want to try and maximise the best chance of reducing the electric in the greenhouse.

I know there will never be a full solution growing under glass will always cost, and will always have to tweak to make it work in all situations.

I shall be saving up to pollycarb the roof first, as long as I can fit it in the glazing strips.


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## Bjorn (Apr 22, 2017)

Ray said:


> We need to be clear on this one (no pun intended): in the industry, "poly" typically refers to polyethylene film, typically 6 mil thickness, UV protected, and often with infrared-trapping-, and/or drip-preventing coatings. Two layers are inflated with a small fan, and that becomes an effective insulating layer. Something you might consider, Blondie.
> 
> The multi wall, rigid stuff - polycarbonate - is referred-to as "polycarb" or just "PC."



Thank you Ray, I meant polycarbonate:sob: sorry for the misunderstandings that might have caused


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## Ray (Apr 22, 2017)

Blondie, as an interim thing, consider a single layer of polyethylene over the exterior of the existing cover. Put some spacers on the existing cover to create a dead-air space, (I have used double-sided cellophane tape to temporarily hold narrow strips of styrofoam), and use tape to seal it to the edges (there is a greenhouse tape available, but good old duct tape works, too).


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## TyroneGenade (Apr 24, 2017)

Hello,

See page 9 of https://web.archive.org/web/2008120....org/newsletters/2007_04AtOSNewsletterWeb.pdf .


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## blondie (Apr 26, 2017)

Very interesting read thanks


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## JAB (Apr 26, 2017)

Million dollar question right? I mean this single query has been the sole reason many an orchid business fail, and the cost to do it properly is so prohibitive that historically only the very well to do can afford to get into orchids on most any level outside a windowsill. 

good luck. Keep us posted on what you decide


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## Bjorn (Apr 27, 2017)

Thanks a lot Tyrone, good reading! Actually I have done similar things, placed a number of water filled containers under the benches, this cools during hot days and release heat during night (= save heating bill) Not a big impact, but measurable. As said before nowadays I use artificial lightnig (mostly due to lack of light in Winter) as the sole heating during daytime.


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## TyroneGenade (Apr 27, 2017)

Bjorn said:


> As said before nowadays I use artificial lightnig (mostly due to lack of light in Winter) as the sole heating during daytime.



How many watts of light in how large a green house? What temperatures do you maintain with this setup?


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## Bjorn (Apr 28, 2017)

TyroneGenade said:


> How many watts of light in how large a green house? What temperatures do you maintain with this setup?



The house is some 27 sqm, and the total wattage lights installed might be around 4000W MH and HPS lighting. Additionally comes a number of LED units (self built and designes approx 200W each)
But when that is said, this amount of lighting is much more than is necessary to lift temperature to approx 20-25C during daytime. In order to avoid "frying" the plants the lights are connected to thermostat that breaks the power when temperature is attained. This thermostat has failed one or two times with ugly results, scorched leaves on the cattleyas etc. Using the lights as heat source works fine, no problem with reduced life of the lights etc.


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## NYEric (Apr 28, 2017)

Bjorn said:


> Thanks a lot Tyrone, good reading! Actually I have done similar things, placed a number of water filled containers under the benches, this cools during hot days and release heat during night (= save heating bill) Not a big impact, but measurable.


Oh, like a heat sink!


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## Ray (Apr 28, 2017)

When I had a greenhouse in South Carolina, I used 12, 55-gallon steel drums, topped with bread flats as my benches in a 14' x 14" double poly-covered structure. The drums were painted black and filled with water and antifreeze (to retard rusting).

Due to the influx of sunlight along the coast (onshore breezes tend to make for extremely clear days) they absorbed so much energy that my electric heater rarely came on.


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## TyroneGenade (Apr 28, 2017)

Bjorn said:


> The house is some 27 sqm, and the total wattage lights installed might be around 4000W MH and HPS lighting. Additionally comes a number of LED units (self built and designes approx 200W each)
> But when that is said, this amount of lighting is much more than is necessary to lift temperature to approx 20-25C during daytime. In order to avoid "frying" the plants the lights are connected to thermostat that breaks the power when temperature is attained. This thermostat has failed one or two times with ugly results, scorched leaves on the cattleyas etc. Using the lights as heat source works fine, no problem with reduced life of the lights etc.



Thanks for the info, Bjorn. Can you please give me some idea of the height of the greenhouse? The maths governing heat loss/gain works on volume, so a W/m3 estimate would be useful. 

MH still give more Lumen/W than LEDs. If the goal was heat then using LEDs would be wiser than MH. From http://www.ledsmagazine.com/articles/2005/05/fact-or-fiction-leds-don-t-produce-heat.html : "The energy consumed by a 100-watt GLS incandescent bulb produces around 12% heat, 83% IR and only 5% visible light. In contrast, a typical LED might produce15% visible light and 85% heat. Especially with high-power LEDs, it is essential to remove this heat through efficient thermal management." It might be feasible to link the LED heat sinks to piping to pump the LED-heat into the water tubs? You can then tone back the lighting and the electric bill.



Ray said:


> Due to the influx of sunlight along the coast (onshore breezes tend to make for extremely clear days) they absorbed so much energy that my electric heater rarely came on.



Winter days here in Iowa are also quite sunny so I am very interested in this solar heating option for greenhouses. No chance of building a greenhouse now but I like to dream... plan! for the future. The problem is that 20+ days of -10 oC weather. And then the 30+ oC summers with near 100% humidity.


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## Bjorn (Apr 28, 2017)

The house is approx.2,6 m high, 3,5 wide and 1.6m at the gables( is that the correct term?) around 7.5 m long if I remember right. However I do not really know the heatloss since that is a function of the temperature difference and the enegy loss. But an indication could be that I am able to maintain an approximate temperature increase of some 25-30C with the lights only. I use MH and HPS because I already had them installed when I added the outer shell of polcarbonate. This covered up the ribs and that made a big difference.

I have been speculating about watercooled leds its perfectly doable, but might not make things easier unless you start from scratch and design accordingly.


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## Happypaphy7 (Apr 28, 2017)

Bjorn- what about the night time temperature control?
Water container (unless it is massive and kept its content rotating) may freeze??


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## Bjorn (Apr 29, 2017)

Happypaphy7 said:


> Bjorn- what about the night time temperature control?
> Water container (unless it is massive and kept its content rotating) may freeze??



The water containers are stored under the benches so hopefully no freeze additionally I have some thermostatically operated heaters, just in case. These run for some time most nights in winter. I have had a couple of power failures and it seems as if it takes more than one day to get down below 5 C even if it is subzero outside.
But generally speaking, our climate is not that bad, except for the long ,dark, winters and cool summers, we rarely have below -5C, mostly around zero.


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## Happypaphy7 (Apr 29, 2017)

That's a lot milder than I thought. 
You must be way down south and near the ocean.


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## Ozpaph (Apr 29, 2017)

Why water cool the LEDS for heating the GH? The heat any lights emit goes into the greenhouse and raises the temperature whether its a into a water heat sink or not. The energy used to drive the pumps might be better spent on aquarium heaters in the water barrels.
The problem I have is exactly the reverse - cooling the enclosed GH for 6-8 months of the year. Layering still applies, though.


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## TyroneGenade (Apr 30, 2017)

Thanks for the info Bjorn.

Ozpaph, those are good points and good ideas. The issue for LEDs is that if they overheat they burn out faster and, before that, their spectrum changes. But still, is it cheaper to find an alternative to cooling the LEDs than pump that heat directly into the water? That is something to ponder as I slowly approach the point where I could build a green house of my own.

Bjorn, your winter conditions are practically tropical compared to mine... It is not unusual to have it at -20 oC for extended periods.


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## Bjorn (May 1, 2017)

I know, many thinks that just because we are far noth it gets utterly cold, that is not the case as you see. But it gets dark.....occasionally we drop to -20 though, but that might be once a year or so. And the winter lasts from November until April, a bit depending on how you define it, and when summer commences, then....it never gets really warm. Around 25-28C is normally the maximum. Summertime it can get warmer further north, beyond the arctic circle.


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## blondie (May 1, 2017)

I'm glad Iasked the question as one forum I got no one answer and that was it.. I will also be pushing to see what other energy providers will charge of the electric, might give the one we are with a shock (pardon the pun). The heatingnhas neber been a problem just a very high increase all over the electric bill and, unfortunately the greenhouse is considered a luxury so would be the first to be scrutinized.

I am stil on the hunt for a pollycarb company that is not asking the odd for the Pollycarb.


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