Heating my greenhouse

kramer56

Ok first post, don't kill me. I need some help with heating my greenhouse with my owb, it is a central boiler e-classic 1450 and my greenhouse is 17x80x12h. I am currently running 3- 125k but can coil units. 2 we're keeping up at 25°f and up. But below that temp my boiler struggles to keep the water above 150 and never shuts down unless of course the wood bridges. I will be getting a bigger 760hdx boiler next season but should I have more water now to help y boiler and will i need more water storage with the 760 hdx next year? If so elaborate and attach photos of possible. I'm up every 2 hours putting wood in it trying to get the water to set point 

Jamie Hall

You won't need more water storage -- but you may simply need more boiler capacity. if I read the specs. for the Classic Edge 760 correctly, it is rated at about 147,000 BTUh over twelve hours. Your three fan coil units can consume 375,000 BTUh; just two consume 250,000 BTUh. There is simply no way you can get more heat out of your fan coils than you put in with the boiler. It doesn't work that way. Even the maximum rated output of that boiler is only 245,000 BTUh -- and two fan coils can consume more than even that.

You will probably need a bigger pump; that much heat at a desirable 20 degree delta T across the fan coils is going to need almost 40 gpm -- but that won't help if the boiler can't power the units.

kramer56

Jamie Hall said:

You won't need more water storage -- but you may simply need more boiler capacity. if I read the specs. for the Classic Edge 760 correctly, it is rated at about 147,000 BTUh over twelve hours. Your three fan coil units can consume 375,000 BTUh; just two consume 250,000 BTUh. There is simply no way you can get more heat out of your fan coils than you put in with the boiler. It doesn't work that way. Even the maximum rated output of that boiler is only 245,000 BTUh -- and two fan coils can consume more than even that. You will probably need a bigger pump; that much heat at a desirable 20 degree delta T across the fan coils is going to need almost 40 gpm -- but that won't help if the boiler can't power the units.

So would a coil in a furnace plenum and a trunk line be more beneficial than the fan coil units?

leonz

Is your greenhouse constructed of glass on a steel frame or stretched plastic film over tubular hoops or structural steel frame over a woven all weather fabric?? Do you have a laundry sink with domestic hot water in your greehouse?

If you have access to Anthracite Coal in your area or sub bituminous stoker coal an anthracite coal stoker boiler will provide you with all the heat and hot water you need and avoid the drudgery of dealing with firewood forever and you can sell your current outdoor wood boiler.

Your heating needs are not all that great; you just need a more effective boiler.

A coal stoker boiler would be a very cost effective way to do this as you could remove the forest eater and use the pad it sits on for the coal stoker as you already have the water piping and electrical wiring hook up there and all you would need to do is build a new shed around the coal stoker to protect it from the weather and have a dry place to dump coal to store it and keep it drier.

Anthracite Coal and Sub Bituminous Coal has more heat energy per pound than firewood and with a coal stoker there is much less handling of fuel.

The ashes would have to be removed every day and the stoker boiler cleaned occasionally but the amount of heat created by the stoker boiler will be more consistent and adding a hot water storage/buffer tank like a surplus bulk milk tank would let you create lots of hot water for heating your green house and domestic hot water using a 170 Degrees Fahrenheit high limit and 150 Degrees Fahrenheit low limit temperature.

In a situation like yours taking advantage of an Axeman Anderson coal stoker boiler 260S model would give you a 260,000 gross BTU rating which would be more than adequate for what you need for heating your greenhouse and you will be able to make lots of domestic hot water if desired; but you would need a plate heat exchanger plumbed into in your greenhouse heating loop if you do not have a domestic hot water loop in your existing systems piping.

kramer56

Stretched plastic with hoops. No domestic in the GH either. 

leonz

An Axeman Anderson 260S coal stoker boiler would save you a lot of work and worry as you would not be out at 3AM feeding it.

The 2 models of Axeman Anderson Anthratube coal stokers which are the 130M and 260M are self feeding as they have an auger which elevates the coal from the coal bin to the firebox of the boiler.

kramer56

And with that I would not need extra water storage or does it come with enough to run 3 heaters feed with 1in PEX

hot_rod

Any idea what the heat load is? Probably not much R value in the covering?

Jamie Hall

Let's go back to the original post: you state that with two fan coils running you were just keeping up at 25 F. If you could get enough heat to run the third fan coil, it could be a good bit colder out and still keep up -- at a guess, down to perhaps 5.

BUT

You still have to provide enough BTUh power in the boiler to run those fan coils. Each of those things needs 125,000 BTUh. Three of them will need almost 400,000 BTUh. You can't fudge that. No jiggery-pokery with extra water will help. A furnace plenum and trunk like won't help. I can't seem to find information on the steady state BTUh output rating of the coal boilers mentioned, but it needs to be at least that figure -- 400,000 BTUh -- to do what is needed.

bburd

Regarding the main piping between the boiler and fan coils, at the usual 20°F temperature difference between supply and return, you need roughly 1 gallon per minute per 10,000 Btuh.  That’s 40 GPM. You will not cram that through a 1 inch pipe no matter what it’s made of; you would need a very powerful pump, the pipe would wear out quickly from erosion and there would be serious  velocity noise. You probably need 1 1/2 inch mains, depending on the distance and fittings in the circuit. And the circulator pump must be selected to deliver that flow rate against the friction head in the circuit.

kramer56

I knew but didn't state it that the 1"pex is a huge factor in my problem and correct no pump can give me the gpm needed home to 1". 
One thing I thought about was run all 3 cans on low speed, yes they don't shut down most likely but the water wouldn't be cooled so quickly as to drop the water temp in boiler. No doubt I'm wrong on that one.

kramer56

I was just wondering if the extra water storage would help the boiler with a different recovery rate or would it make it worse into disaster mode. 
Those propane heaters they sell for GH has to be a fast recovery time is the only reason to use them opposed to boiler systems. If I had the recovery I think the issue would be gone or almost tolerable if it is there.

bburd

You seem to be trying to compensate for insufficient boiler capacity by storing some of the heat in a tank.

If you were heating tap water for ordinary uses, that would be an effective strategy; but you are heating a building. The demand for full heating capacity in severely cold weather will go on for much longer than any reasonably sized tank would give you.

You’re gonna need a bigger boiler. 

kramer56

Correct I do need and will be getting a bigger boiler this summer. When I put that in, should I expand per say the water amount of the boiler capacity or leave it the way it comes.

mattmia2

Lower speed will reduce condensation and sooting and corrosion in the boiler by increasing return water temps but it will do nothing to solve your insufficient heat problem. You are trying to violate the first law of thermodynamics, you will only get out as much heat as you put in.

Jamie Hall

kramer56 said:

Correct I do need and will be getting a bigger boiler this summer. When I put that in, should I expand per say the water amount of the boiler capacity or leave it the way it comes.

Leave it the way it comes. There's no need to expand it. What is the steady state heat output of the new boiler? You need around 400,000 BTUh.

leonz

Edited today 3/30/22

(If you have access to either an Sub Bituminous Stoker Coal supplier or an Anthracite Coal supplier to obtain Anthracite Pea Coal I candidly think using an Axeman Anderson 130M coal stoker to make steam to feed a small herd of surplus steam radiators set in the center of your greenhouse with a Steam Thermostatic Regulating Vvalve would be the best way to heat it).


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Are the fan coils piped in series or piped separately with thier own heating loops??

With that much demand you would either have to have two Axeman Anderson 260S units in series or an
Alternate Heating Systems S500 coal stoker making 180 degree water or a third option would be to use a surplus 8,000-30,000 gallon insulated railroad tank car and then use a single 130M Axeman Anderson stoker and heat the water to 170 degrees to create 8,000 gallons of thermal mass that you can strip with a shell and tube heat exchanger and one circulator to feed all three water to air heaters.

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A more cost effective way to do this would be to use a single Axeman Anderson 130M to make dry steam using a double drop header to feed dry steam to a steam to air garage heaters in addition to a new fan hung in the hoop stays. The stoker would have to be in its own shed and the steam piping to the green house would have to be insulated.
All the steel piping in the greenhouse would have to be insulated to prevent the heat from the steel pipe melting the plastic roof if it is hung in the hoop stays.
A coal stoker making steam heats one drop of water and expands 1,700+ times to provide heat via radiators or a steam to air coil heating system.
A double drop header lets the dry steam expand twice before it wanders off to pass through the header pipe or pipes and then to the radiators where the dry steam pushes the atmospheric air out of the radiators and the vents close and the radiators stay hotter longer.
Can you afford to lose a bit of floor space in the center of the green house?
You could use surplus cast iron steam radiators for steam heating.
You would be able to use a steam TRV on the last steam radiator to control the temperature of the green house and make use of the thermal mass of the surplus steam radiators.

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In regard to hot water heating, if you heated 8,000 gallons of 50 degree well water to 180 degrees Fahrenheit you need a temperature rise of 130 degrees.

If you used a 4 gallon per minute circulator to push the hot water through the stoker and then on to the 8,000 gallon tank car it would take 2,000 minutes/33 hours for one complete exchange, .

If a 6 gallon per minute circulator is used it would take a little over 22 hours for one complete exchange of cold well for hot water out of the coal stoker.

If a surplus insulated coiled railroad tank is used the exchange is faster as the internal heating coil is used as the heating method for the 8,000 gallons of well water in the surplus insulated railroad tank car.
The hot water coming from the stoker boiler never contacts the water mass in the tank car and returns to the boiler to be circulated in a closed loop between the stoker boiler and the green house.

A small circulator could be used to push 8 gallons per minute through the green house heaters in series and then returned to the tank car to be heated using a top draw method to take advantage of the upper hot water layer in the tank car.
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This becomes a bit more confusing with an insulated tank car without a coil. The hot water circulated from the coal stoker to the tank car will rise to the top and the cooler water will settle to the bottom and be drawn into the return line header of the coal stoker.

The atmosperic vent tapping in the tank car could be taken advantage of by installing a drilled well casing cap used for jet pumps which makes use of two tapping's/openings in the well casing cap for the circulator installing one longer pipe for the return to the bottom of the tank car and the shorter pipe for the suction side of the circulator avoiding the use of the bottom drain of the tank car.

A mercury float switch would be used to make sure the water level in the tank car is monitored using a mercury float switch to shut the circulator off if the water level in the tank car gets too low.
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A coal stoker boiler making hot water for heating or steam operates using a hold fire timer sequence which activates the stoker and combustion fan to keep the fire lit and the coal burning once the hot water reaches the high limit temperature of 180 degrees and the coal stoker will go to the hold fire sequence in temperature only operating to maintain a 180 degree temperature in the boilers hot water jacket and then the timer will stop running the boiler when the number of minutes set on the timer dial with the timer pins goes past the last timer pin.

The hold fire timer is over ridden if a heat call drops the water temperature in the boiler to the low limit temperature and the stoker begins operating again where the induced draft fan in the 130M coal stoker starts and the viewing door flap is pulled shut sealing the firebox and the combustion air begins entering the boiler through the bottom of the ash pit and the coal fire begins burning once more and the rolling grate begins moving forward and at the same time the coal auger starts and lifts the pea coal up to the transfer head and it drops into the coal feed tube where it stays until the rolling grate pushes the dead ash off the grate and allows more fresh coal to drop on the fire while there is a heat call.
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The helix screw that the 130M and 260M use prevents any excess coal from causing a coal fire as the unburned coal that traveled up the helix falls back down to the bottom to be lifted again to the transfer head and then into the coal tube above the coal grate that rolls back and forth as the coal burns and the dead ash is pushed off the end of the rolling grate into the ash pan.

Using the current buried and insulated tubing and the concrete pad the OWB sits on would work well but the coal stoker would need to be protected from the weather with a hoop shed that would also provide cover for the coal supply.

The end wall would have to be solid using a wood wall or cinderblocks or the hoop shed could be raised using the large cast concrete blocks and a clay thimble mudded into the gap between two cast concrete blocks using a 5" or 6" clay thimble for either the 130M or 260M to allow the flue pipe to exit and then rise vertically using a rain cap.

The green house would benefit from hot water storage of some type even with the coal stoker because of the inherent heat loss.

If you google AHS coal stoker in Montana it will link you to several you tube videos describing
how coal mine electrician replaced an outdoor wood boiler with AHS S130 to heat his home and hot water using Montana mined Sub Bituminous Stoker Coal to heat his home and make all his domestic hot water.


I hope I have made less of a mess with my editing and adding more detail.

Leon

leonz

I would like to add this fuel comparison chart to the
greenhouse heating discussion to add more information.

leonz

I neglected to add this yesterday,

If you used a steam certified coal stoker boiler you could employ a double drop header to make lots of dry steam heat.

kramer56 said:

And with that I would not need extra water storage or does it come with enough to run 3 heaters feed with 1in PEX

Solid_Fuel_Man

A plastic sheeted greenhouse is basically like heating the outdoors when the sun isn't out....

The 3 fan coils are likely enough to keep the plants from freezing. 

However you need the horsepower, not the flywheel. Storage is just a flywheel, if you don't have the horsepower (heat input) to keep the flywheel spinning fast enough (high enough water temp) then nothing will compensate for that. 

You also need a bigger driveshaft (pex size) to convey that horsepower. 

You have several things which need to be addressed to make this work. 

You have some options:

1. Reduce the heatloss of the greenhouse, glass is better than plastic....then you may be able to get by with what you currently have....maybe

2. Install at least one more run of 1" pex to convey more heat....if you can generate that heat. 

3. Get more heat, bigger boiler (forest eater) and the pex to move the heat. 

4. You could also use a supplemental heat source, a woodstove in the greenhouse. Plenty of fans on it! Or propane, or fuel oil, or coal, or.....you get the idea. 

scott w.

If you have neighbors, they are gonna hate you if you burn coal. My grandmother had a coal furnace when I was a kid......the black smoke would pour out of the chimney when that old monster was at peak firing. Black soot would land on the snow around the house in winter.

leonz

To clarify this,

Scott w, you are very wrong in your statement about smoke with Anthracite Coal.

Bituminous coal smokes exactly as you describe when using a hand fed boiler or furnace using a manual draft control and shaker grates.

Deep mined Anthracite coal, reclaimed anthracite coal stripped and washed from old previously mined Anthracite Coal mines and Deep anthracite coal mined in the southern United States, Sub Bituminous Coal and the Sub Bituminous coal from the Powder River Basin of Wyoming, Montana and Alaska or the Western Canadian provinces does not smoke like the Eastern Bituminous Soft Coal that your grandmothers furnace used and everyone who is reading this thread needs to know this.