Heating a Greenhouse

Grallert

So. I've been giving extra job of managing the greenhouse here on campus. One of the things we've done during our western mass winters is plug in a bunch of electric oil filled radiators. This seems like it might not be needed. The space consists of a glass house 31' long 19' wide 10' from floor to ceiling. with 36' block walls. Attached to the glass house and open to it on one side is a "potting" shed. This is 21' x 21' and floor to ceiling 12" on a 36" block walls.
The whole space is heated with approximately 100' of 1" fin tube in a parallel format with a 155k WM mod con.
My question is: Is there a recommended heat loss program for green houses? Our design day is -10 or so with an interior minimum point of 50. I don't know but I imagine that the installer did the math and I would like to not have to use the space heaters.
Any input would be helpful.
Stay calm and carrot on...
M

SlamDunk

download the app from slantfin.    

Big Ed_4

Not being a farmer but worked on greenhouses in my past , hanging space heaters seems to be the heater of choice , They are compacted and uses a fan to throw out them BTUs.
Base board only uses the natural convection . They are low , easily damaged , dirt and blockage impedes on its output.. .

Over the years, thoughts of greenhouses using radiant heat potting platforms pops up on this board . Not being a farmer but is seems like a good Idea keeping the soil at its proper temperature . It may be a good school project . Get engineering involved

Always do a heat loss calculation to your zone to know the minimum needed .

Grallert

As it stands now the emitters are commercial fintube under the planting benches. Unfortunately the 40' or so in the "potting shed" are impinged by stuff the previous has stored underneath. She's still a big presents here and kind of a hoarder so clearing it all out is challenging at best. If I can convince leadership that the cost of a storage shed could be offset by the savings resulting from eliminating the impingement to the convectors and eliminating the need for the space heaters smiles all around.

Grallert

SlamDunk said:

download the app from slantfin.    

I have it but didn't even look to see if there's a greenhouse option. I'll do that now.

SlamDunk

You have to fudge a little. Inusalation, nil. Windows 25'x25'.

hot_rod

https://greenhouseinfo.com/calculators/

EdTheHeaterMan

I have worked on 3 different customers with green houses in southern New Jersey. Three different farmers 4 different green houses. All of the greenhouses used an oil fired furnace connected to a plastic bag that was flat when the fan was off. When the furnace, operated, the plastic bag inflated. There were 3 to 4" holes cut into the plastic bag every 12" or so for the length of the bag that went from one end of the green house to the other. The largest green house was about 40' x 80' about 20 ft high. That used a commercial furnace that had a firing rate of about 3.50 to 4.00 GPH. The other three were somewhat smaller with the same "plastic bag duct" system and they were 1.10 GPH or less normal residential furnaces you might find in a low basement or crawlspace.

These three farmers must have used the same furnace man before they started using me for burner service. I don't recall ever needing to replace the large 20" diameter bag duct in the several years that I serviced the green houses.

Looking at the heat loss calculator provided by @hot_rod, it seams that the furnace sizes and the green house sizes were pretty close.

hot_rod

I think unit heaters are used for cost and quick recovery.

But hot air rises so the heat will be up high against a cold roof/ ceiling.

Radiant may be a bit more efficient as it heats objects not air. Its easier to move around and at much lower SWT.

Rutgers in NJ is one of the leading authorities on greenhouse application, root bed heating, etc. Maybe sniff around that site at the horticultural engineering department.

Grallert

Quick heatloss from greenhouse info.com gives me between 90K and 100K. With a 155K boiler I should be able to set this up to satisfy the demand. Time for some tweaking.

Paul Pollets

A suspended gas fired unit heater would be far less expensive. Of course you could do radiant under the grow areas and a unit heater for the air temps for maximum production.

Grallert

So the system is in. Has been for about 15 years. I'll be attempting to balance it for an even 55* on a design day. That's about -10 in our parts.