heating greenhouse

[Engelkefarm]

i have a 20x50 ft greenhouse 6 inch concrete floor with 2 inch insulation and radiant floor.i have a wood boiler its a energy mate and a propane boiler i also had the plan to use a unit heater as a way to dump extra heat if necessary i hooked everything up the other day boilers in series. the return from the floor into wood boiler into gas boiler up to the unit heater and then into the floor. the unit heater is hooked to an aqua stat so if temps got above 160 the fan would kick on and put out heat. my problem is keeping temps up the cold return to wood boiler was about 60 degrees wood boiler would heat that to about 110-120 then the gas boiler would heat it to about 150 the unit heater never kicked on. floor supply temp after mixing valve was 110 and return 70. i had system running about 5 hours. pumps were constantly running should i hook them up to aquastat? i think my main problem is too cold of a return but how do i solve that? i

 

[maple1]

It will take a long time to get that concrete up to temp.

 

[Engelkefarm]

Would having a primary and secondary loop help?

 

[Karl_northwind]

Yes. and a return mixing valve or pump on the wood boiler side.

 

[Karl_northwind]

Look up Caleffi's Idronics publication series, and number 10 in particular. it will give you a lot of options. in short, your wood boiler is a high temperature device, as is your fan convector. the radiant slab is a low temperature system, and to make them play happily together, you need some mixing (for the floor) and boiler protection for the wood boiler. I don't know what your gas boiler is, but if not a mod-con, will need some pumping or mixing too.
karl

 

[Karl_northwind]

Just noticed that you have a mixing valve for the floor, so nix that part of the sentence. long day, I'm usually here during the morning when I'm all bright and shiny.

 

[Engelkefarm]

I would think a mixing valve returned to wood boiler would more or less just circulating around rather than putting out usable heat?

 

[Engelkefarm]

diagrams and links would be great. i have looked at a bunch but it seems like there are alot of different setups

 

[Karl_northwind]

but it keeps the wood boiler from condensing, creosoting up, and dying an untimely death.

 

[Karl_northwind]

Hydronics for Wood-Fired Heat Sources - Caleffi

 

[Engelkefarm]

diagram 7-10 you are talking about?

 

[Karl_northwind]

Yes, if you have buffer tanks, that would be an ideal sort of configuration. you can have 2 separate loops pulling off the storage tanks, one with a mixing valve set to 150 for the unit heater, and one set to 120 or so for the in-floor.

what sort of LP boiler do you have in this system?

 

[NE Properties]

Hydronics for Wood-Fired Heat Sources - Caleffi

What a great resource. Thank You!