Heat Pumps

[Alan McKnight]

Has anyone used or know of anyone that is using a heat pump to heat/cool a green house.

I have a split system I put in my wife's office and it works great in the summer and winter.

It is maintaining a 400 SF area. cost was under $1000.00.

[Susie Gehri]

Tell us more Alan....

[Paul Trudeau]

Alan, I don't know of anyone, but I do know I'd make sure the GH was insulated to the max before looking into heating it.

[Alan McKnight]

I don'at understand the question. What info are you asking for?

Susie Gehri said:

Tell us more Alan....

[Susie Gehri]

I guess you had a plan for how this would work. but I certainly respect anything Paul says, and MY greenhouse definitely is NOT insulated by any means....

[Alan McKnight]

How a Mini-Split Works Some people do not have any knowledge of what a split system is as it is not a common item in the US. Europe has used this type of system for years.

Like conventional HVAC systems,   the noisy compressor and condenser is outside the house. But Split systems eliminate the need for a basement- or attic-located evaporator unit and bulky ductwork by using thin copper tubing that pumps refrigerant directly to discreet wall mounted blowers inside. Even more remarkable, this same unit works in reverse in winter, absorbing heat from the outside air and moving it indoors to heat your home. The result? Efficient cooling and heating for year-round, whole-house comfort in most climates.  Available in numerous mix-and-match capacities and configurations, there's a  mini-split systems for even the most difficult to heat and cool areas. Easy Installation Copper tubing running through a small 3 to 4-inch opening in the wall or ceiling easily connects the indoor and outdoor units. Refrigerant is cycled through the lines from the outdoor condensing unit to the indoor unit, where the air is quietly distributed to the interior space. Aesthetically Pleasing Conventional air duct systems tend to be bulky and can require special structural attention while Halcyon system piping can often be routed through walls and joists to maintain aesthetics. Flexible, Remote Control Cooling Because each room has its own handler, you can create up to four zones with a timer and optional wired remote that puts you in temperature control and allowsyou to meet the varying comfort needs of different spaces.

Installation is as simple as 1, 2, 3… 1. Mount indoor and outdoor units. 2. Connect refrigerant and drain lines. 3. Make electrical connections.  An easy installation for contractors  saves consumers time and money.

I did all the install myself including the electrical except the Freon hookup when I installed it in my wife's office. I would go with a 220 volt unit as they are more efficient the the 120 volt units.

Susie Gehri said:

I guess you had a plan for how this would work. but I certainly respect anything Paul says, and MY greenhouse definitely is NOT insulated by any means....

[Bob Campbell]

I think it would be way too expensive to simply heat or cool the air in the green house if the extracted heat were wasted. But if you have a use for hot water in the Summer or cold water in the Winter I suppose it could be justified. 

My experience has been that Summer heat is not a problem if you ventilate and Winter heating can be accomplished with a stainless steel resistive heater.  Planting season appropriate crops is IMHO the best way to go.   The fish can tolerate cooler than optimal temperatures in the Winter and there should be no problem in the Summer if good ventilation is provided.

In fact I removed the rather expensive evaporation cooler pads on my insulated garden room, and opted for simple ventilation this Summer after calculating the expense of running the fan for that system.   Everything worked out fine.   I'll double check my log but as I recall the water never rose above 78F.

Only if the crop provides enough value to offset the high cost of temperature control would this type of system be practical.

Even tomatoes will grow well in cool air if the roots are kept at about 72F.  This can be accomplished with a stainless steel resistive heater at a moderate utility cost if you insulate, and provide supplemental light to lengthen the day.  Ceramic Metal Halide bulbs provide good penetration into the crop's canopy, and will also provide heat to the air and therefore should not be considered as wasted heat. 

[Alan McKnight]

Bob, I agree with  you on cooling costs a a good fan and a swamp cooler should work. However heating is another issue. Resistant heat is the most expensive type of heating there is, (at least in my area). These new split systems are getting SEER ratings of over 19, so that is really efficient.

I just threw this topic out there to see what the responses are and also to learn from the group.

[Bob Campbell]

I see what you are saying.  It's difficult to imagine heat begin extracted from cold Winter air to heat an even warmer space, but you are right.  It would be an expensive initial cost, but payback may be worth the investment.

By the way I said the evaporative cooling turned out to be unnecessary when good ventilation is used.

[Alan McKnight]

Oops missed that line evaporation cooling turned out to be unnecessary when good ventilation is used.I know it is hard to imagine extracting heat from cold air, but remember that you are using Freon that is colder then the outside air (down to about 15 degrees) so there is heat to be drawn into the liquid.  True they don't work real well below freezing, but we don't have that many days below freezing in our areas.

[Bob Campbell]

I'm still thinking on this.

 

The cost of a small heat pump is not bad, but I imagine a non insulated green house will require a fairly large heat pump. A 10000 BTU heat pump would probably not do much on a freezing cold night.

But if the water is kept at a good temperature, and all but the south side is insulated then the air will stay warm.  As long as 40-50 degrees air temperatures can be maintained then it is probably OK for most plants.

By the way, I am not real happy with the way I did my glazing.  I feel that a small part of the East and West wall should also be glazed to capture the morning and late afternoon Sun.  (I also use a horizontal shutter to keep the heat in during the night and reflect extra light in by day.)  If you would like to see my systems I posted a video a few days ago.

So it might work if the heat pump were to heat the water.  And if you were to modify it that way, then maybe a solar heated water reservoir .for the outside heat source could also be incorporated.  Sort of like a ground water heat source heat pump.

But in the end you have to be realistic about the investment you are making.  If it's just a few vegetables and some fish then you have to ask yourself how much that is worth.  Besides if this is your passion then feeding a rocket mass stove may not be such a bad idea.  If it's a large commercial green house then feeding the stove could just be a duty.   Plus a rocket mass stove keeps you independent from the utility company.

Alan McKnight said:

Oops missed that line evaporation cooling turned out to be unnecessary when good ventilation is used.I know it is hard to imagine extracting heat from cold air, but remember that you are using Freon that is colder then the outside air (down to about 15 degrees) so there is heat to be drawn into the liquid.  True they don't work real well below freezing, but we don't have that many days below freezing in our areas.