Design Temperature Help Needed

 
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Post by NoSmoke » Tue. Dec. 06, 2016 7:16 am

You guys know me, I cannot help but add onto my house every year and subsequently add another zone to my radiant floor heating system. This year it was a small change, just the laying of radiant floor pex under my mudroom tiled floor to heat my 9 x 12 mud room. However now my heating system is out of balance again.

I have a variable speed mixing valve coming off my main boiler loop connected to a Taco 705-2 PLC. The main boiler is a 80,000 BTU propane wall hung Munchkin Boiler that I am only heating 2400 square feet of well insulated house with.

I really want my finished mudroom to be part of my great room, but when I took out the door between them, the great room (on its own zone with thermostat, zone valve and separate manifold with flow controls for the pex; stayed at 67 degrees which was always a degree below its set temperature of 68. So no big deal I thought, up the design temperature and it will settle out.

Nope, it did not work.

I upped the design temperature by a whopping 10 degrees and it still did not work. For radiant heat they recommend an in floor temp of 140 degrees and I am up to 145 degrees! Yikes. Still my boiler was running constantly to try and heat the mud room/great room and could only pull it to 67 degrees; 1 degree shy of set temp. The other rooms in the house, consisting of 2 zones that heat a 28 x 40 addition, had no issues reaching set temp, and in fact were never on. With such hot water flowing through the floor, they came up to temp quickly.

So I reinstalled the door between the great room and the mudroom. Instantly my Great Room is up to temperature and the boiler never runs at all.

But I am not sure this is the way my system is supposed to run. I am thinking since I sent my design temperature so high, I am basically bypassing the function of the Taco 705-2 PLC and just running via thermostats and zone valves. I am thinking the real culprit is that I am asking too much from the great room zone. The mudroom is just sucking up enough heat (as small as it is) that the boiler is struggling to heat that room. Since that first zone has four loops of pex, and the second zone 3 loops of pex, and the third zone only two loops of pex; maybe moving the mudroom pex to the third zone that only has two loops of pex to try and distribute the load better.

So my questions are:
Is my design temperature set too high since my boiler is running via thermostat instead of PLC?
Should I redistribute my pex loops?

(There may be other issues too, like the pex going to my mudroom not be buried in concrete (exposed to the air) for 15 feet or so before entering the concrete in the floor there, but that seems doubtful. I will say, you guys are my only hope. My boiler tech guys know nothing about these systems and simply told me "rip it out and put in something we can understand." Screw that!!

This is what I mean by great room, it is wide open...
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Post by Rob R. » Tue. Dec. 06, 2016 8:28 am

Is the mudroom an addition with 3 exposed walls and roof? If so the heat loss is probably quite high, and may be beyond the capability of your radiant slab...with the door open, it just adds to the heat load of the great room.

Run the numbers to see what the heat load of the mud room is, and compare to the output of the floor (you need to measure the surface temperature of the floor) You may discover that a little extra oomph is needed. A two stage thermostat with a cast iron radiator in the mudroom would be nice...or you could add a radiant ceiling.

 
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Post by coaledsweat » Tue. Dec. 06, 2016 9:01 am

The slab should be insulated with a vapour barrier. Without that, you will be giving up a lot of heat to the earth below. It will take a very long time to normalize.

 
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Post by NoSmoke » Tue. Dec. 06, 2016 3:36 pm

I am not sure exactly what you mean by exposed?

If you mean it juts out on its own as a structure onto the main house, then yes it is exposed, but if you mean uninsulated, then no it is well insulated. The walls are only R-11 because the mudroom was a shed over at my grandmothers house that I hauled across the road and put into place as a mudroom. Anything I build ALWAYs has 2 x 6 walls, but that is not the case here. Still the ceiling is super insulated with 15 inches of fiberglass insulation (R-49). No vapor barrier on the floor though. :-(

I will have to go through that room and see if I can tighten it up even more.

But would you lower the design temperature setting now that the mudroom is isolated from the great room with a door?

 
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Post by CapeCoaler » Tue. Dec. 06, 2016 6:25 pm

How is the floor insulated in the mud room?...
Can you add some foam sheet to bring up the r-value of the walls?...
Spray foam would tighten up the old shed too...
Just one inch of foam would seal for infiltration...
DIY foamer kits abound...

 
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Post by Rob R. » Tue. Dec. 06, 2016 8:09 pm

The temperature of the water in the tubing is only a means to an end. It is the temperature of the floor that matters. If you have ceramic tile for a floor, I would think 140 degrees would be plenty, but a quick shot with an infrared thermometer would tell the real story.

Did you bother to calculate the heat load of the mud room before you decided how the heating system should be designed?

 
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Post by NoSmoke » Tue. Dec. 06, 2016 9:27 pm

Well it depends on what you mean by heating system design.

The boiler was already in place and I just tied into an existing manifold so in that regard I did not calculate for anything. If you mean designing the spacing of the radiant tubing, we spaced them really tight on the outer walls (about 6 inches apart) and then about a foot apart on the inside. This is what I did for the rest of my house so I guess I just assumed it would work. Honestly I never thought much about the small footprint not being big enough to heat it.

I cannot give you an exact temperature reading on the floor, but it is warm enough so you feel it when you are wearing socks, and more so barefoot of course.

With the door shut now between the great room and mudroom, the temperature swings fluctuate greatly. That is because the call for heat in the other rooms are not calling for heat during the day and so the mudroom gets no heat, but at night when the boiler comes on (it is 22 degrees tonight), it warms the floor.


 
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Post by Sting » Tue. Dec. 06, 2016 9:50 pm

I think it may be time for a new and expanded sermon on System Balancing. But that's just me! :D
What temp is the water returning from the slab vs going to it?

 
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Post by Rob R. » Tue. Dec. 06, 2016 10:09 pm

I think I misunderstood. The mud room is not on its own zone?

 
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Post by NoSmoke » Wed. Dec. 07, 2016 7:01 am

Sting wrote: What temp is the water returning from the slab vs going to it?
My system is quite complex, utilizing a variable speed circulator driven by a computer (Taco 705-2 PLC controller) to adjust the temperature. It does this via four sensors; temperature outside, temperature of the slab, return water temperature coming back from pex loops, and main boiler temperature; checking them all once per minute. With that it calculates just how much heat the slab is losing.

The colder it is outside, naturally the home (and slab) will lose more heat so it compensates by increasing the temperature of the water running through the floor. This is called target temperature. When the outside temperature goes up, the reverse happens because the home (and slab) loses less heat and so it requires less less hot water flowing through the floor to maintain set temperature.

The design temperature is named, not because it is pumping water through the floor at whatever it is you set it at (in my case 145 degrees), but rather just a number to help calibrate the computer. Two years ago it was set at 100 degrees because I was only heating 1120 square feet with it. But last year when I nearly doubled it to heating 2080 square feet, I had to bump the design temperature up to 125 degrees to compensate for the extra load. This year when I added my mudroom, I assumed upping my design temperature again would work.

It hasn't.

I have also fussed with my flow controls to each individual loop, slowing down the water flowing through the floor in the mudroom to extract more heat. It is flowing a mere 1/8 of a cubic foot per minute so I am gleaning about all the heat I can out of the floor.

I guess what I am concerned about is the design temperature being so high that it is throwing my computerized system out of whack. It basically is eliminating the role the PLC makes in controlling the heat in my house via the PLC and instead controlling the heat by the thermostats and zone valves. That is NOT the way my system is supposed to run. The thermostats are only supposed to tell the system there is a call for heat, the zone valves and circulators should always be open and running, and the room temperature controlled by how warm the water is flowing through through the pipes. That would be the most efficient I think because the variable speed circulator (mixing valve) would be running at less capacity, drawing less water out of the main boiler loop. Ultimately it is more efficient because you are only using the minimum number of BTU's to heat the house to the desired temperature.

 
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Post by Sting » Wed. Dec. 07, 2016 7:14 am

NoSmoke wrote: I have also fussed with my flow controls to each individual loop, slowing down the water flowing through the floor in the mudroom to extract more heat. It is flowing a mere 1/8 of a cubic foot per minute so I am gleaning about all the heat I can out of the floor.
Your running 140 degrees supply temp water to an in floor loop at that low of a flow rate? :?

How long is that loop or loops in feet of pex?
What size is the pex?
again - what is the return temperature of that loop or loops of that zone?

 
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Post by NoSmoke » Wed. Dec. 07, 2016 7:15 am

Rob R. wrote:I think I misunderstood. The mud room is not on its own zone?
No it is not on its own zone at all. It is tied in with the Great Room Zone. I think you are right though, if it was, because of its lack of heating surface, and heat loss, it really needs it. In that case if it was cold (north side of the house with only exterior doors for windows), and the rest of the house was warm, warm water would continue to be pumped into the floor.

I thought having the door removed between the two rooms would help equalize the heat. That did not happen, it only made the heat loss for the great room so great that the room never reached set temperature.

I am thinking now I would do better if I cut the design temperature down to 135 degrees, let warm water be pumped through the floor more often and see how the mudroom does.

It is not obnoxious now. Ideally it would be an addition off the great room without a door, but with a door, as long as it is above freezing we are okay with that. Just someplace to remove and store shoes and jackets so the Great Room is not so cluttered up.

It very well may be I must add a new manifold to the boiler, along with zone controller and thermostat to really get the mud room to heat properly. An interim measure I can take is to candle and seal up every stinking draft I get. Another alternative is...since this mudroom consists of two rooms, the first being heated and the second outer room not...to insulate that room and help protect the mudroom (the first room) more.

 
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Post by NoSmoke » Wed. Dec. 07, 2016 7:24 am

Sting wrote:Your running 140 degrees supply temp water to an in floor loop at that low of a flow rate? :? How long is that loop or loops in feet of pex? What size is the pex?
again - what is the return temperature of that loop or loops of that zone?
(1) No, as I said it is variable. The design temperature just calibrates the computer for what would be the highest anticipated load.

(2) I just checked the computer and at 26 degrees outside it has a target temperature mix of 115 degrees. As the temp rises throughout the day, the water flowing through the floor will go down. If it was to drop to 22 degrees, it will go up.

(3) The pex is 1/2" and 200 feet long.

(4) I cannot tell you the temp of that exact loop, but the manifold temperature is Delta-T, or 95 degrees. That is how I ball park my flow controls on the manifold. I slowed the mud room control a bit more to extract more heat. It also has less footage then the other loops that are in my Great Room.

 
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Post by Rob R. » Wed. Dec. 07, 2016 8:24 am

I would put the mudroom on its own zone.

I have a greatroom that is an addition, the heat load of just that room is nearly as much as the rest of the house.

 
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Post by Sting » Wed. Dec. 07, 2016 9:04 am

115 in
95 out

looks good to me

follow Robs advice

Kind Regards
Sting


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