Radiant heating in Greenhouse Should I use Glycol?

Joebif

I have a radiant heating system using PEX in several places as heat exchangers to warm the water in our Fish tanks.  Should we use Glycol in the system to stop the system from freezing? The greenhouse will have a wood stove in it and I may add 2 stoves in case the first can't keep it above freezing.  But We probably will not be able to constantly keep a fire going in it so what do you all think?



How does it get put into the system? Any thoughts?

Joebif

Tested last night need help

I had temperatures down to 34 last night.  I setup Aqua-stats on the fish tanks and plant troughs. At 8:00 PM I had 61 degrees in both places. At 8:00 AM I had 59 in the Fish tank and 52 in the plant troughs. I had all the pumps off so the heat would not be even, I will be having the pumps on all night so that will be another test. The temperatures for both will go up to 70 so the fish can survive.



This was just allowing the water to be stagnate with no foam insulation on the top of anything. I think with the R7 Insulation on the plant troughs it will be a lot less of a heat loss. I would think I might gain 1 degree on the fish tank but will wait and see. I will be testing that soon. The fish tank is 4' deep and the plant troughs are 1' deep. The data shows that the bigger the depth of water the lower the loss of heat.



If the fish tanks and troughs say only loose 1 degree or 2 with insulation and foam insulation on the top my PEX going out to the greenhouse could freeze if none of the zone valves go on. The PEX under the troughs and tanks will be fine becasue they are under warm water. I have a walkway that has a 1" PEX supply and 1" PEX return with the connections at 5/8".



I could use propylene Glycol or wrap and insulate the pipes but not sure if that insulation would be enough. Or turn up the set point to make sure that everything gets warmed a few degrees thus having 140 degree water in both the supply and return.



Would love to hear  some experts on the subject. Not sure if having a leak under the pool liner were the PEX  is would be a problem to the fish. If the water does not leak out I would not think that the Glycol could leek in at all.

Mark Eatherton

In your case....

You could force all of the fluid out of the system and determine how many gallons of fluid the system holds, then pump a 1/3 solution of glycol back into the system. I prefer to premix my glycol and pump it in as I am filling the system.



You'd have to have a fill and purge set up, which is basically a ball valve with a drain cock on either side. Close the ball valve, and pump in one valve, and out the other back to the mixing bucket.



The toxicity of propylene glycol is low for humans, but not sure about the corrosion inhibitors and their affect on fish. Best check with an aquatics bioengineer before deciding.



ME

PeterNH

Freezing

Hello Joe,

Here is my low budget, non-professional solution.

This is how i keep my pex connected, copper fin baseboard in the glass porch and garage from freezing:

I do have zone valves not individual circulators and my boiler is 6 feet lower in the basement of the house. Possible you might have a similar setup?

The thermostats in the garage and porch set to 45'. series connected to a double pole refrigerator control with the sensor mounted outside.  The control is set to 36', above that everything stays turned off, below 36 outside,  the inside thermostat has control.  The trick is the end switches on the zone valves are disconnected, thus a slow, nearly constant gravity flow of hot water, run by the low limit settings, (125-150) on the aquastat,  comes up, circulates around and goes back down at at around 110',  never a freeze up even though it can get below 30 in either space.  When a zone in the house calls, the pump runs and things heat up a lot more and even if the thermostats satisfy, there is enough heat around the pipes to keep things from freezing up until they call for heat again.    There are three toggle switches, one to bypass the outside control and the others to reconnect the end switches if i need more heat to work on a project in the garage.

One of these years i going to have the boys at the local oil co set up a plate heat exchanger, with gylcol, a pump and expansion tank etc.

But for now it's been reliable for the last 8-9 years. In spite of some -15 degrees nights. The porch is uninsulated and the garage is poor: 3" in the walls, 9 ceiling and nothing under the slab.

  A side benefit is this also helps to reduce short cycling as the additional cooler water from the garage and porch slow down the recoery of the boiler when a house zone calls.



Peter

Joebif

Thanks for the info

I have been testing with foam on top of the troughs and insulation on top of the fish tanks and only lost 1 degree last night. It got down to about 34 so not bad. The nice thing is I am not loosing that much heat in the water which is fantastic. That means all the PEX underneath the water will stay at least the same as the water above it. The other thing is the system may not kick in at all or I may just need to adjust the set points every night unless I can find a temperature that is just right. Then if it heats up only 1 degree I may not use that many BTU's but 5000 gallons of water to heat 1 degree could be more than I think. I am not sure what that is.



ME I am not sure but so far I am not getting anything back from the aquatic people that looks good. They just do not want to take a chance at having a problem so I may try this without Glycol.



I have about 40' of 1" PEX that is warmed by the sun during the day and I could insulate it. It will be covered after I get a few more things done but will have exposure from the side. I looked into heat tape and wire but not sure if it would be okay to use. I would like to find a reasonable source for it as well.



Then again when my storage tank and wood stove gets finished I may get enough hot water in the storage tank every night to take care of a 1 or 2 degree increase. Or build a solar panel or 2 and use the heat from the sun in the storage tank for the 1 or 2 degrees at night that might be needed. As we get colder nights this may change but so far so good.

PeterNH

5000 gallons

Then if it heats up only 1 degree I may not use that many BTU's but 5000 gallons of water to heat 1 degree could be more than I think. I am not sure what that is.

It would take about 41,727 btu's net at the water to raise it 1 degree.

Not counting losses at and around the boiler, in the piping along the way or losses underneath and to the side of the pex heating pipes. All of which are likely a significant percentage.



Sorry i missed where you are located but around here in Souther New Hampshire and "exposed" pex water pipe will freeze in a heartbeat when it sustains below freezing cold air.

Hard to visualize the environment of the 40 foot of pipe.

Any pictures?



Peter

Joebif

No Photos yet

It is a walkway that I am building and there is 20' of supply and 20' of return.



If my tanks and troughs are at 61 degrees right now and I set my aqua stat to 61 then during the night when I loose 1 degree my zone valves will turn on and then 140 degree water will flow through the PEX keeping the PEX from freezing I would think.



I have a water heater for the boiler and it is a 55,000 BTU heater so what Peter is saying then is that I would have only one hour of heat usage or a bout 3/4 of a gallon of propane given that I am about 85% efficient on the gas. So if my Aqua stats come on at different times(there are 4) then I would stand a good chance of always having hot water in my PEX and maybe no freezing at all. 



Is that possible?

PeterNH

insulation

Hello Joe,

Two things come to mind.

1 Constant circulation with a 3 way mixing valve

2 Heat Tape and  insulation.

Insuation would be a good idea in any case.

The good old boys around here that have outside wood boilers have a good method of insulating underground pipes:

dig a trench

build a box out of pressure treated lumber.to hold,

 the pipes covered with 1/2 or larger round foam pipe insulation.

insulate inside the box with at least 2 inches of closed cell styrofoam insulation all around,  with the foam insuated pipes inside.the wood and styrofoamed box.

In your case i'd do the same thing only with thermostatically controlled heat tape on the pipes before putting on the round foam.



One other question, if there is 61 degree or so water returing to your water heater,  what about flue gas condensation destroying the inside of the water heater?



Peter

Joebif

61 degrees is the temperature in the fish tanks.

I am maintaining that temperature right now but will be going to 70 degrees after I get the wood boiler on line.  I will be adding the wood boiler next and putting the heat I get from that to a 500 gallon storage tank with a heat exchanger to the propane heater. The wood boiler is an open system. Then I will be using a mixing valve and 2 zone valves. One zone valve normally open that will have a aqua stat on it that if the temperature in the storage tank is greater than 140 stays open. The other zone valve is normally closed connected to the propane heater so if the storage tank is lower than 140 opens to use the propane heater. The mixing valve will keep it at 140 so if it is higher it will not harm the propane heater. The water heater is set up using 140 supply and 130 return. I have a variable speed pump on the whole system and it keeps it at a Delta T of 10.



Where is a good source to get reasonably priced heat tape and insulation?

PeterNH

NONE. NADA. ZIP. Capeche?

Hello Joe,

Looking over your posts to try and understand what you have and i see something that gives pause.



In this thread:

http://www.heatinghelp.com/forum-thread/137836/Adding-to-new-setup-need-help

the final drawing has a zone valve and what looks like two ball valves



Brings back this bit of advice from Mr M. Eatherton, here:

http://www.heatinghelp.com/forum-thread/137500/Is-this-safe

 

An "OPEN" system defined...

An open system can not be pressurized.



In your example, in the piping circuit from the barrel stove coil going to the storage tank with the immersed heat exchanger coil, immediately after the stove coil you will have a full port tee with the side branch facing up. The end of this upward pipe will have to go at least 5' above the highest part of the system served. You will need to increase the size of the pipe to accept the expanding heated water, otherwise expect spillage and a continual need to replenish the water level.



The pump will be place between the vent tee and the tank heat exchanger. There shall be NO isolation valves of ANY sort in this circuit. NONE, ZIP, NADA. Capeche?



All components in this circuit will have to be metal of a non ferrous nature, or stainless steel.



You are going to have to figure out how to snuff the flame on power failure, and how to keep the pump running (UPS) after a power failure to avoid coil stagnation and steam kick.









what's up with ignoring such sage advise ?





Peter

Joebif

Advise has been taken and a new system was made

In the post by me called new drawing I re-did everything and put in a pressurized side and a non-pressurized side to the open system.Then I added to this just yesterday a new drawing that has not been posted yet but will put it here so you can see what I have. It has 2 zone valves and the mixing valve. It has a controller and a normally open valve and a normally closed valve at #2 & #3. The controller works them both so if the storage tank is warmer than the set-point of the propane heater it leaves it alone. If the storage tank is lower than the set-point of the water heater it closes and opens to the propane side. The mixing valve keeps it at the same set-point as the propane side.



This has a open storage 500 gallon tank connected per ME's advise with a battery backed up pump and a controller. The controller works and turns on the pump as soon as any heat comes from the wood stove. It is connected via a gravity feed and has the battery backup with all of the necessary precautions keeping it open with no pressure. The wood stove will only be fired in the evening 1 time. The battery backup is designed to last 8 hours for the pumps wattage ratting if anything should fail. The wood stove will only be fired with small fires. If the wood stove puts out too much heat a fan coil dump zone will be put in place.  The pump is a 3 speed pump and will be used by the controller and adjusted to regulate the heat.



The pressurized side will have a heat exchanger in the storage tank.



So far with all of my tests and the cold temperatures we are having today and I will see how it does, predicted to be a high of 27 today and 13 tonight, I may not even use the wood stove for water heat that much at all. I have been monitoring it from my PC and see that the fish tanks and water troughs have only called for heat once each last night. That means I have maybe used 1/2 to 3/4 of a gallon of propane so far. That is fantastic. With all the sun we get in Colorado my tanks have been able to maintain the 60 - 61 degrees.



All the storage tank needs to have in it then is temperatures of 140 to 160 degrees. With the tanks only needing maybe 45,000 to 90,000 BTU's per night this should be enough to keep the tanks at the desired temperatures. I will also add a solar water panel(s) to the storage tank next year. Then I will gain more than enough water temperatures in the storage tank and probably turn off the wood stove water heating capabilities forever. I will be monitoring this and building this very slowly and will be very cautious. The greenhouse is not growing anything in it  and is 300 feet away from the house and I am not trying to heat this up fast but slow and easy to see what we get and what it does.

PeterNH

ok

Joe

I think i understand.

My mind was playing tricks on me 'cause i thought those two handle looking things near the pump at R1 look like ball valve shut off's and the .posibility that they might accidentally be shut off - coud be catastrophic. Scared me.



As far as heat tape goes, search around for it, it shoud be affordable.

Same goes for insulation.  Lowe's, Home Depot, local buiding supply/hardware stores sometimes have sales this time of year.  But it's usually only the 3/8 stuff on sale

My local hardware store had some tan colored 5/8" on sale last year. 

It can always be found at Pex Supplly, but often times a local sale could be a better value.

I've never used heat tape on pex, just copper. So no clue as to the best method.  I've read to wrap the pex with aluminum foil and run one or two wires lengthwise along the pipe, top and bottom, then insulate it. Othere say to wrap around the pipe.  Hopefully someone here knows the best way to do it.



Peter

Joebif

You are correct

Those 2 handle looking things are ball valves so I can disconnect the pump some day if it fails so I can get a new one in easily. The only thing I could do there is wire them open so they can't be closed or find a padlock for them and I only have the key or something like that.



The other thing I have noticed today, becasue it is snowing here pretty hard, is that the snow is falling off the greenhouse roof plastic constantly. Last year I did not have the water in the fish tanks and troughs and that did not ever happen until the sun came out the next day. With the 5000 gallons of 61 degree water my greenhouse is much warmer as seen by the snow falling off the roof.



I can't wait to see how this does with the wood stove in there.

Jean-David Beyer

wire them open

Youy could open them full, and then take the handles off. Put them somewhere where meddlesome fingers cannot find them.

PeterNH

300

Hello Joe,

With the 5000 gallons of 61 degree water my greenhouse is much warmer as seen by the snow falling off the roof.



I can't wait to see how this does with the wood stove in there.





Man 300 days of sunshine, what am i doing staying in NH.



Anyway if all the sun is keeping your tanks warm almost by itself, then your pipes are going to get so little use, they are surely going to freeze. Best to have a plan for it.

Real soon now.



Peter

PeterNH

opps

Joebif

Yes but!!

So far with the 5000 gallons of 61 degree water, the greenhouse is way warmer than the outside. It is 33 now outside and 50 in the greenhouse.