shop floor heat help please

jtpfarm

I'm new here but hopefully someone can help me. I have a 60 X 40 farm shop. It has one large single zone of floor heat. There is 1800 ft of 3/4 inch pex split up into 6 runs. I have a 100,000 btu corn burning boiler with a primary/secondary loop system. I'm in Minnesota so it can get pretty cold.

Here is my problem. When it gets down in the teens or single digits especially over night, my boiler can't keep up. I absolutely cannot get my return temperature over about 73 degrees which leaves my floor at about 62 and my air at only 54. My water going into my floor is about 82. The boiler is running 170 degrees but I have to mix it down to keep the stove warm. If I run any more than 82 the stove will cool off quickly and the aquastat will shut the pump off until it warms back up.

Here's my question. My boiler holds 18 gallons of water but the rest of my system holds more than that. Would it help to have a storage tank so I have enough hot water stored up to run through the whole system?

Or any other suggestions? Any help is appreciated. Thanks

kcopp

Was the floor underneath and sides of the slab insulated? if so w/ what?
What are you using for Circulator pumps?
How long are the loops? 300'?
What are the centers?
How thick is the slab?
Got pictures?
BTU's are btu's..the storage will not help you too much. Somehow the load is too big OR the BTU are as ME says thermally constipated in the boiler.

Harvey Ramer

The big temperature swings you are experiencing are due to the lack of insulation or air sealing. If the slab is uninsulated or poorly insulated, you have to get the building shell just as tight and well insulated as possible in order to avoid the temp fluctuations.

It also helps to run the slab on and ODR (outdoor reset curve)

In some cases it may be necessary to hang a Modine from the ceiling to supplement the load during rapid outdoor temperature declines.

Harvey

SWEI

Yeas to both of the above -- has anyone done a heat loss calculation? 300 foot loops of 3/4" PEX have very low flow resistance -- 82˚F supply water is on the cool side unless this is a very well insulated structure.

SWEI

Much of Minnesota has affordable electricity. I'd tighten the envelope as much as practical and give some thought to an electric boiler for the baseload.

jtpfarm

Thanks for the responses so far.

To answer some of the questions above:
The slab is somewhat insulated. It has insulation underneath around the outside but none in the middle. Its kind of a unique situation. The building had a previous floor in it that was un even. Below my slab is 3 inches of gravel. below that gravel is another 6 inches of cement.

I have a small taco pump on the primary loop which is 1-1/4. The primary loop has a larger Bell & Gosset pump on it and is 1 inch. (im not sure of the exact pump specs)

My loops are 300' on 16" centers.

The slab is 7 inches thick in the middle and thins to 4 inches at the wall.

I realize BTU are BTU. My thoughts were that the mass of my boiler was too small in relation to my floor.

Keep in mind, I am no expert on hydronics. Here was my thought process:

(this is just an example)Say I had a boiler that only held 1 gallon of water and a system that holds 20. During they day (average day) my water sits in the floor because I don't require much heat and goes down to the floor temp of 62 degrees. Once I require heat, the pump kicks in and that 1 gallon boiler has to heat 20 gallons of water up from 64 degrees. Would it not have trouble at any btu due to the large amount of water being returned to a small amount of heat area?

It just seems to me that the amount of cool water coming back to my boiler is too large of a volume compared to the volume of my boiler. I thought if I had enough BTU stored up during the day that I could pump a bunch through all at once to actually get my return temps to rise. Which in turn would allow me to run higher input temps.

Also keep in mind that with the corn boiler, even with no call for heat, the boiler is always burning on low fire. It needs to burn for 3 minutes every 10 minutes to keep itself burning. On days in the 20s with minimal wind, if my thermostat is at 56, it will be close to 60 by the end of the day due to extra heat being made. That was also part of my storage tank theory.

Im sure my thought process is not how it actually works so please correct me where needed. Thanks!

jtpfarm

SWEI said:

Much of Minnesota has affordable electricity. I'd tighten the envelope as much as practical and give some thought to an electric boiler for the baseload.

In my opinion, If you grow your own corn, there is not really any other heat source that is cheaper. A neighbor just put up a 70 x 90 shop. Best of everything as far as under slab insulation and spray foamed entire structure. He has electric heat one year before he went to a waste oil burner. The cost was just outrageous for electric.

Harvey Ramer

In your current situation the best bet is tone put in a 2 stage thermostat and a Modine heater on the 2ND stage for a quick pick me up. If you pump the volume of btu's into the poorly insulated slab, that it takes to follow the weather pattern, you will overshoot setpoint temp by a large margin on an almost daily basis.

jtpfarm

I would be fine with setting the temp at 60 and letting it go to 65-68 during the day. That's when I work in there. My main concern is to be able to try to keep the boiler from running continuous over night.

The main reason I started thinking of this is because a friend of mine has a storage tank that he is no longer using. It would be free but Im trying to determine if its worth my time to install it.

Harvey Ramer

Having the boiler run all night doesn't hurt a thing. I don't think you really realize the amount of water storage it would take to keep the boiler from running all night. It would be a tremendous amount!!!!

KC_Jones

Just to clarify what the OP is trying to do. Are you trying to do night time setback with this setup?

jtpfarm

So is there anything I can do to improve my system as it is?
As far as the way its plumbed or the way it operates?

jtpfarm

KC_Jones said:

Just to clarify what the OP is trying to do. Are you trying to do night time setback with this setup?

If a night time setback is an option, I would be open to that

KC_Jones

I only mention it because with slabs like this setbacks are a bad idea. You mentioned not running at night and that sounded like you were trying to do a setback. High mass systems like this work best with a constant temperature setting.

jtpfarm

I don't want it to not run at night. Id just like to give the boiler a break overnight. With the corn stove, long run periods create excessive clinker build up on the burn pot. A 20 minute break would help a lot.

jtpfarm

Here is my crude drawing of my setup

SWEI

Change the mixing valve to a Taco iSeries-R valve (3-way or 4-way) and see how that works. Can you keep the place at a constant 55˚F? 50˚F? If not, you can try a timer-based setback of a few degrees by switching a resistor in parallel with the OAT thermistor. I haven't done the math, but a second thermistor might actually work better.

Harvey Ramer

Well there is a little here and a little there you can do.

First, with a little change you can get slightly more heat out of the boiler and help to improve indoor temp swings to some degree. Install a 2-way I-series ODR mixing valve and replace your manual valve with a real balancing valve . Follow the Taco manual to a T on the setup. And yes, a 3/4" 2-way Mix valve will give you up to 400,000 BTU capacity, going from a high temp boiler to low temp radiant. Say 180° to 120°. It won't have the flow restriction of a 3-way valve.

Every little thing you can do to tighten up the shop will help a lot.

As far as the boiler running all night, I don't see why you couldn't put in a 24hr timer that would shut off the call for heat at intervals of your choosing.

jtpfarm

Thanks for the input so far guys.

Can someone explain to me what the 2 way mixing valve and real balancing valve actually do?

SWEI

The 2-way valve would be a direct replacement for your existing mix valve. A 3-way would isolate your distribution system better and allow constant circulation. A 4-way would replace the closely-spaced tees and do the same. All of them would be controlled by ODR, which will eliminate the "cold water in the slab" problem and avoid overshoot.

jtpfarm

After reading some of the diagrams on the 2 way ODR, I think part of my problem is that my tees are 6 inches apart. (more than 4 times the diameter).

If someone could draw me a diagram of how these valves would be plumbed in I would really appreciate it. (its easier for me to picture it that way) Thanks again everyone.

Harvey Ramer

Click on the link in my previous post, the blue words, and that will take you to the manual. The manual has diagrams and all the instructions.

SWEI

...but the manual shows closely spaced tees with the 4-way, which most of us don't believe are required for most systems.

jtpfarm

Is it a problem that my tees are too far apart if I add these parts?

Harvey Ramer

Some solid fuel boilers are not very conducive to the slow flow rates produced by the 4-way without a boiler circ. Those same boilers, it is critical to wire in an overheat dump zone. I am not familiar enough with corn fuel to draw an accurate conclusion of whether it would be needed in this case. I have 2 monster coal boilers that I take care of. They will start boiling in minutes if the circs are shut off.

I do agree with you though. With most conventional boilers, I have no qualms deleting the boiler circ and closely spaced tees.

I this man's situation, with the uninsulated slab, the measures we have suggested will be an improvement but not a complete fix. I have dealt with uninsulated slabs before and there is only so much you can do to maintain temp control. The heat sink under the slab just becomes to massive. They all operate in the same fashion. They run all night and stay shut off all day.

With that in mind, I would maintain the boiler loop for the purpose of adding in a Modine to buffer the cold spells.

jtpfarm

What is the Modine you are talking about?

Harvey Ramer

If your tees aren't more than 6" apart you won't have any trouble. Just make sure you don't have them reversed.

Harvey Ramer

Something like thishttp://www.modinehvac.com/web/Hot-Dawg/Hot-Dawg-H2O.htm#.VIJV2cso7qA or thishttp://www.modinehvac.com/web/Commercial-HVAC/SteamHot-Water-Unit-Heaters/Horizontal-Hydronic-Unit-Heater.htm#.VIJWr8so7qA

jtpfarm

Would it be beneficial to use that and the floor heat together?

jtpfarm

Also, how would I plumb that in?

Harvey Ramer

Absolutely! Use a 2 stage thermostat. 1st stage being the floor and 2nd stage turns on the Modine to supplement the building when needed. The Modine should be first in line on the boiler loop so it gets the hottest water.

jtpfarm

So I would pull off the primary loop with 2 tees and another pump? Mixing valve or not?

jtpfarm

Would it make sense to set it up so that after the floor heat runs for say an hour that it would kick the modine in?

Could I use a night setback with this setup?

Harvey Ramer

No, not really. A 2 stage thermostat would turn the Modine on and off on an as needed basis while leaving the floor heat running.

Night setback is never a viable option with radiant floor in a concrete slab.

SWEI

As he indicated, Harvey and I are not actually disagreeing here. I was not actually suggesting removal of the boiler circ, just questioning the need for closely-spaced tees given that the 4-way valve provides its own form of hydraulic separation. Either the 3-way or the 4-way will also provide boiler return temp protection (DIP switch #3).

SWEI

The hybrid approach would be to use the boiler and the radiant to maintain a base indoor temperature as I indicated above (say 50˚F) then fire the Modine when you're actually using the space. You might even skip the two-stage stat and just install a timer. An electronic one programmed to your planned occupancy schedule or even an old fashioned twist timer might work for you.

jtpfarm

Thanks very much for all the help guys, I will try the modine.

Couple last questions.

1, Do I need any sort of mixing valve to run the modine? And where would I hook it in the system.

2, If in the future I install a larger boiler, will my floor heat work any better or am I still going to need the modine?

Gordy

Your floor tubing holds 34 gal +\- . What is the circulator size for the floor loops?

Harvey Ramer

jtpfarm said:

Couple last questions.

1, Do I need any sort of mixing valve to run the modine? And where would I hook it in the system.

2, If in the future I install a larger boiler, will my floor heat work any better or am I still going to need the modine?

You don't need any mixing valve for the Modine. Just put a pair of closely spaced tees in the boiler loop upstream of the floor heating circuit. With the addition of the Modine, you need the electronic mix valve on the radiant more than ever. The reason being, it will provide adequate boiler protection from the radiant zone even with the fluctuating supply temperatures caused by the modine turning on and off.

By the way, what is the btu load on the boiler? And what temp does it keep the shop say when you have 0° weather for a week?
You need to establish a baseline to get an idea of the size for the Modine.

Harvey

Tim Potter

Just in case you need extra homework for extra credit....

http://www.caleffi.com/sites/default/files/coll_attach_file/idronics_10.pdf

A ton of info in that publication

For what it worth, I also have a high temp heat source connected to low temp radiant, I was advised to use the ESBE Thermic (there are other brands of the same style device, Hot Rod & SWEI have 2 that come to mind) to protect the boiler, It works like a charm to protect the boiler on the 2 systems I have then installed on.

Tim

jtpfarm

Harvey Ramer said:

jtpfarm said:

You don't need any mixing valve for the Modine. Just put a pair of closely spaced tees in the boiler loop upstream of the floor heating circuit. With the addition of the Modine, you need the electronic mix valve on the radiant more than ever. The reason being, it will provide adequate boiler protection from the radiant zone even with the fluctuating supply temperatures caused by the modine turning on and off.

By the way, what is the btu load on the boiler? And what temp does it keep the shop say when you have 0° weather for a week?
You need to establish a baseline to get an idea of the size for the Modine.

Harvey

How do I find the BTU load? If it is 0 for a week it will keep it about 53 degrees