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Author Topic: Need to cycle my pump on and off?  (Read 4367 times)

slimchance

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Need to cycle my pump on and off?
« on: November 22, 2017, 12:04:24 PM »

I have a Hardy H2, heating the concrete floor of a 40x60 shop/house combo.  I have an 8 circuit, manual flow control manifold, I would like to add a thermostat to my system so that it will shut off my pump when my in-house temp gets to a certain point, then the pump will come back on when needed.  The floor holds the heat very well, but is seems like I need to slow down my burn cycles.  I have my aquastat turned down to 160 from 170.  The aqua stat turns the blower on/off.  I have most of my manifold valves just slightly turned, feeding as little as 0.2 GPM per circut.  As it is now, water entering my manifold is about 155 degrees, and exits the manifold at about 85 degrees.  It seems like it is all I can do to get a 12 hour burn, but yet I really don't need all of the the heat it is providing the floor.  I'm just looking for suggestions. Currently, with very little cold weather so far, "garage" temp has been around 72 degrees and the "living" space has been around 74 degrees.  Wife likes the temps, but I feel like I could slow my burns down and save some wood.
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hondaracer2oo4

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Re: Need to cycle my pump on and off?
« Reply #1 on: November 22, 2017, 08:32:01 PM »

Woowwwww. You are going to have a problem with the concrete soon if you don't stop heating the floor with 160 degree water. The radiant system Needs a tempering valve on it. It needs 80-90 degree input temps. Please head over to radianttec.com and read their information on radiant heating.
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hondaracer2oo4

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Re: Need to cycle my pump on and off?
« Reply #2 on: November 22, 2017, 08:35:01 PM »

Oh and you shouldn't be running your minimum boiler temp below 160. You shouldn't have boiler return temps less than 30 degrees from when they left the boiler. Temps below 140 entering a boiler cause condensation on the inside of the firebox which mixes with ash to create and acid and eat the metal.
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E Yoder

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Re: Need to cycle my pump on and off?
« Reply #3 on: November 22, 2017, 09:07:57 PM »

I doubt condensation would harm a 304 SS Hardy- but, yes it definitely needs tempered down water feeding the floor..way way too hot. Wood consumption should drop, temp swings stabilize, and you protect the concrete.
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E Yoder

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Re: Need to cycle my pump on and off?
« Reply #4 on: November 22, 2017, 09:10:50 PM »

But I'm.forgetting you asked about a thermostat... Yes, the stat can start and stop the pump using a relay. A 90-340 or 90-370 would work.
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wreckit87

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Re: Need to cycle my pump on and off?
« Reply #5 on: November 22, 2017, 09:26:51 PM »

Oh dear. My advice, put a 40 plate exchanger in the boiler loop near the manifolds and close up the radiant side of the exchanger so it is a separate, closed system with its own air separator, expansion tank, mixing valve, and pump while the boiler loop continues to circulate constantly, keeping the plate hot at all times. That new pump would be controlled by a wall thermostat and you could adjust flow output between the house and shop portions using the flowmeters on the manifold if you wanted the house a bit warmer. I just did this for a customer a couple days ago as he had a similar consumption issue and REALLY hot floors. Spoke with him this afternoon to see how it was going and he said he was going to hug me next time he sees me. Supposedly wood consumption is cut in half, AND his forced air coil is actually useful for the first time in 11 years since the floor isn't robbing 98% of the heat. Totally redefined his entire heating system with $450 worth of parts. Definitely something to think about. Boiler water in a slab is never a good idea. A few folks out there will use a 4 way mixing valve or an injection pump to run their floors, but the cost of that mess ends up being just as high or higher than just doing it right the first time, plus a closed system keeps oxidation out of the floor loops which plugs them up over time, and the typical 12psi a closed system runs at is far easier on the pump to circulate instead of "pushing" like they do in an open system, raising efficiency
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hondaracer2oo4

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Re: Need to cycle my pump on and off?
« Reply #6 on: November 22, 2017, 09:34:20 PM »

I would tend to agree Eldon on the condensation but I had a hardy H4 that I ran for 4 years. It was 23 years old when I took it out of service. When I bought it used in 2011 it was missing a good portion of the bottom of the boiler floor in the firebox. I could only assume that it was from sitting every summer without a cap on the chimney and rain water getting in and mixing with the ash to create the acid and eating the floor away. This is just my theory though
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shepherd boy

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Re: Need to cycle my pump on and off?
« Reply #7 on: November 23, 2017, 04:18:47 AM »

 Still coming out of a flat plate without a mixer could still be too hot.  Done a lot direct out of boiler with a mixer that worked great. Pressurization with a flat plat can help you with air bleeding but I try to stay away from all the extra equipment when I can. Just my opinion.
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E Yoder

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Re: Need to cycle my pump on and off?
« Reply #8 on: November 23, 2017, 05:21:58 AM »

I was thinking the same thing, mixing temp down would need to be done even with a flat plate? Maybe I missed something.
Interesting Honda. Wet ashes aren't good..
« Last Edit: November 23, 2017, 06:21:53 AM by E Yoder »
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wreckit87

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Re: Need to cycle my pump on and off?
« Reply #9 on: November 23, 2017, 06:55:26 AM »

I assume you're both referring to my comment. If so, yes- you both missed something. Mixing valve was mentioned and is necessary for proper radiant slab operation. I figured since Honda already commented on the target water temps, I'd leave that part out
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wreckit87

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Re: Need to cycle my pump on and off?
« Reply #10 on: November 23, 2017, 07:44:53 AM »

Out of curiosity gentlemen, when you pipe a 3 way into the boiler loop to serve a floor, what happens to flow in that loop when the zone valve for the floor opens? 8 loops for example, 2400 sq ft, average insulation, we're looking at 4-6 GPM necessary to properly heat said floor with tempered water. The typical 1" PEX underground can only carry 7 GPM total, so you have 1-3 GPM or 10-30k BTU left in your main loop. Mama's doing laundry and needs some hot water or all 4 kids run through the shower; there goes whatever was left. Then your forced air calls or the unit heater in the garage calls; oh dang, there's nothing left, why not? It'd be different if a radiant floor only ran for 5 minutes like forced air does, but with proper water temps a floor will run for several hours straight, robbing 2/3 of your available BTU. Being separated with a plate, that floor only uses its own water to heat and passes it through the exchanger to heat it instead of physically using the boiler's water to circulate through the floor. This maintains a constant 7 GPM through the boiler loop regardless of load, and allows it to replenish several times faster while still keeping everything satisfied. I specialize in radiant floors and have yet to see an atmospheric system perform anything like a closed when there are other things in the loop. It's not that I'm closed minded, I really would like to see an atmospheric system prosper to simplify the installation process but the fact is that it doesn't. Even if the floor is the only thing in that loop, a guy still needs a 4 way  mixer or at least a 3 way zone valve plus a 3 way mixer to get flow without deadheading the boiler pump right? Perhaps I'm missing something but of the dozens I've swapped to closed, exactly zero of them performed worth a crap the other way and I can't see how they could
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RSI

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Re: Need to cycle my pump on and off?
« Reply #11 on: November 23, 2017, 11:53:27 AM »

If the radiant is setup as a secondary loop, it can't deadhead the main loop. Only 3 way thermostatic valve and pump is needed.
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wreckit87

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Re: Need to cycle my pump on and off?
« Reply #12 on: November 23, 2017, 01:57:01 PM »

Completely overlooked that, thanks. Still doesn't fix the rest of the problems though. Even set up as a P/S, you're still taking 4-6 of your 7 GPM from the primary loop in the aforementioned scenario. Say it's 10 or 12 loops even, you have nothing left. 100% of your boiler water goes through the floor. For the extra $225 upfront, I see absolutely no reason to potentially double your wood consumption and have a poor performing heating system UNLESS there is nothing else being served. Even then, I certainly wouldn't want oxidized boiler water in my inaccessible slab but to each their own. Just trying to get a grasp on why people do this
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slimchance

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Re: Need to cycle my pump on and off?
« Reply #13 on: November 23, 2017, 02:14:32 PM »

Thanks for all the information, looks like I have missed a few steps in my system design. What will happen to my concrete with current setup?
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juddspaintballs

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Re: Need to cycle my pump on and off?
« Reply #14 on: November 23, 2017, 02:16:11 PM »

wreckit87, the way you setup a radiant system makes sense to me and I am following along on your points.  I've never done radiant anything so far, so I really don't know much about them.  Your point about robbing the flow from the main loop makes perfect sense and whenever I do radiant floors in my house, I'll certainly be using a closed loop with a plate exchanger and a mixing valve. 
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