How do greenhouse growers keep heating costs down

[NYEric]

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!

 

[Ray]

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.

 

[TyroneGenade]

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.

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.

 

[Bjorn]

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.

 

[Happypaphy7]

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

 

[Bjorn]

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.

 

[Happypaphy7]

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

 

[Ozpaph]

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.

 

[TyroneGenade]

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.

 

[Bjorn]

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.

 

[blondie]

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.