Newhouse Farm

john cliff

Hello
Has anyone tried to install a heat sump in a commercial size glasshouse - 10 metres by 4.5 and 3.6 metres to the ridge?
I have a spec for such an installation in a small greenhouse but by how much do I need to uprate the specification for a larger model.

John

Tanya · Posted: Fri Oct 02, 2009 9:07 pm Post subject:

Moved to gardening in the hope that it gets seen by folk here.
Tanya

Mike&Penny · Posted: Sat Oct 03, 2009 1:24 am Post subject: area

Compute the area (total surface area) of the small green house and divide that into the total area of the large one. Multiply by the volume of the heat sump of the small greenhouse to get the volume needed for the large one.
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Hex · Elm Sapling Joined: 12 Dec 2008 Posts: 60

The largest i know of is under a greenhouse 96ft x 45ft x 15ft high. It uses 5700ft of buried tubing driven by 3x 1920cfm fans.
I have ~200ft of tubing installed under mine (154sq ft floor, 900cubic foot volume) which can drop 30C air temps down to 17C using a flowrate of 675cfm.

Edit: I crunched a few numbers to give an idea of a starting point assuming the greenhouse has a volume of ~4300cubic feet.
Divide the floor area into two sections and install 240ft of tubing in each section. Use a 12" (870cfm - 150w) duct fan for each section for a maximum of 21 complete greenhouse airchanges per hour (add a fan speed controller for flexibility).
The air will spend approx 0.81 seconds underground, doesn`t sound like very a long time i know but it doesnt need to be..mine takes just 0.66 seconds to drop 13C.
Performance wise, assuming the air entering the tubes is 30C and the air exiting the tubes is 17C.. you be banking about 13kw per hour into the soil mass for an electrical cost of 300w/hr or a COP of 43.
Knock on benefits are lowered dayime humidity and internal air movement so you don`t have the expense of buying or running additional HAF fans or an exhaust fan.

MrBean · Elm Sapling Joined: 29 Jun 2009 Posts: 35

Sorry to be pedantic, but do you mean 13kWh per hour? 13kW per hour doesn't mean much. That's still a lot of heat to store, what depth do you have the pipes at, and what temperature does the soil rise to?