Enough boiler ?

WcIAfarmshop · January 2

NHB150

ODR Set to 5 (high mass radiant) max@10 degrees F., min @ 60 degrees F.

Air thermostat (On-off)

6" slab fully enclosed w 2"pink

39 300' ½" loops, approx 6"oc,

60'x102' , fully spray foamed

Ironman · January 2

Getting the ODR properly set to match the load is the best thing that you can do. Set the thermostat to 1cph.

WcIAfarmshop · January 2

I have a simple on off thermostat , no cycle-per-hour setting available

WcIAfarmshop · January 2

Never seems to get to the water temp it's calling for unless the primary pump is on low (grundfos26-99)

WcIAfarmshop · January 29

This is my first floor heat experience. I really like the feel of it, just like to know more about it to make it better.

Learned a lot already on this site. This seems like the only place to get advice or ideas.

hot_rod · January 29

Is it heating the shop adequately now?

6120 square feet at a rough guestimate of 25 btu/ sq ft would need 153,000 on the coldest days. If that is a 150,00 input boiler, maybe 135,000 output you may fall short on some days. Or indoor temperature drops. But a heat load calc would be a better "guesstimate"

I like the 6" oc spacing, that was a good investment, especially with a 6" thick slab.

GroundUp · January 29

If it's keeping the thermostat satisfied, it's big enough. If the target water temp is higher than necessary, it's not uncommon to never reach it- very likely your ODR curve needs adjustment. With 6" OC tubing, even on the coldest day of the year your water temp should never need to exceed about 100* so if it's much higher than that, it should come down anyway.

hot_rod · January 29

If the tube is at the bottom of that 6" pour it may need to run a bit hotter SWT, or take a smaller output per sq ft. This example was for a 4" slab 100 SWT with12" oc. The 6" oc will help also.

tube depth.png

WcIAfarmshop · January 29

If I remember correctly my heat load came out to 113k , @ a design temp of -2degrees Fahrenheit , indoor temp of 70

WcIAfarmshop · January 30

https://forum.heatinghelp.com/discussion/comment/1831338#Comment_1831338

Also, the boiler seems to run near 100% capacity unless the primary loop pump is on low or medium. Is that normal not to be using much of the turn down ratio?

hot_rod · January 30

https://forum.heatinghelp.com/discussion/comment/1838841#Comment_1838841

that would be 18 btu/ sq foot. That is a nice number for a large shop. Your boiler is large enough and you have plenty of tubing. ODR on low temperature systems will not add a lot to the efficiency. But if you have it, may as well dial it in.

Getting it perfect takes some tinkering. If you have an actual design it will indicate SWT on design day, start with that number at the high end. If not guess something like 105 as a WAG

On some of the mod con boilers they have a boost function. If the boiler is not keeping up with the load based on temperature rise, it will automatically raise the supply temperature.

So read the control manual to see what functions your control can offer.

WcIAfarmshop · January 30

I had a design done , called for 115 swt, but it was with 12"oc , and the designer forgot about the open ceiling. I don't know how far off that would throw the design temperature.

Also , it does have a boost feature and a custom ODR feature

Tom_133 · January 30

you got pics of the install, and what size are the pumps feeding the floor?

ratio · January 30

It may take a week to bring the slab up to temperature, as well. What's the delta?

GroundUp · January 30

https://forum.heatinghelp.com/discussion/comment/1838865#Comment_1838865

Again, that's because the SWT is too high. Any boiler will run 100% until it reaches the desired setpoint so if the setpoint is too high, it'll never modulate which is what you're seeing. Turn the temp down.

WcIAfarmshop · January 30

Grundfos 15-58 on the loops

hot_rod · January 30

70 could be too warm if you are doing any physical work in the shop?

With an 82 degree floor surface, 70 ambient, you get just at 25 btu/ square ft.

With 1/2 tube on 6” spacing you could probably run .5 gpm per loop.
39 loops at .5 gpm 19.5 gpm for the pump spec

a 6” slab that size is around 113 yards of concrete, 452,000 lbs. so it may take time ramp up, and down. The ODR will help prevent overshoot., and having a massive flywheel to tame down

WcIAfarmshop · January 30

https://forum.heatinghelp.com/discussion/comment/1838913#Comment_1838913

System has been in operation for a month

Delta at the manifold is 10 to 13

hot_rod · January 30

at days end, it’s the load on the building that drives the operating condition of the boiler. Not unlike a tractor plowing a field.

The boiler will seek and find a thermal equilibrium point, based on the load. The delta is fine, and if it continues to stay at that, neither supply or return temperature moving, you have reached thermal equilibrium

If the boiler runs non stop under that condition, the floor is taking 100% of its horsepower.

If the shop heating as you expected? Have you had a cold/ design day?

WcIAfarmshop · January 30

Cold day design was -2 , 70 indoor temp.

I only have it set to 64 or working becomes too warm.

Just did the design @70 so I would know the capability if ever needed.

Floor surface temp is usually right around 70.

With a good solar gain day their is no call for heat

Tom_133 · January 31

I dont think you are in bad shape at all. I have a Baxi 133K in a shop thats 60x80. Not spray foamed, just the rolled insulation. It has 3" of foam underneath and we put the tubing on top of the rebar so only 2" down from the top. It works great. The return temp is always low, the slab only needs to get to 65 keep it at 60 in there which is what he wants. Design day is -20 with 20 mile an hour wind up here in Vt. I may have gone a little bigger on the boiler but it was a good used one I had kicking around. I think your setup will run for long stretches if you wanna go up 5 degrees in the building, but if you set it and forget it, you should be ok

WcIAfarmshop · February 4

Thanks, I'm still wrapping my head around the modulation and outdoor reset lol. If I bump the thermostat a degree it will run for 45-55 mins. Usually 71-73 on the return manifold.

Ive been told it's like a smoker "low and slow" for best results.

hot_rod · February 4

To raise the room temperature, the floor temperature needs to be increased. So to add even 1° to that nearly 1/2 million lbs of concrete will take some time. A slab like that behaves more like a freight train than a race car.

Actually, you do want the boiler to run a long cycle like that instead is short bursts.

The ODR control tries to match the boiler supply temperature to the load, by basing it on the outside temperature. By doing this you can help avoid over-shooting the temperature to and in the slab.

It sounds like the system is purring along? Any problems with it's performance?

WcIAfarmshop · February 6

The more I understand the system , the more I realize that it is functioning exactly as designed. Just a stark difference from my residential air-air heat pump.

newinnj · February 7

hi I have the same exact boiler as yours. The discussion board helped me figure out something with the boost function. The boost function turned on and then the call for heat is done and the elapsed time finishes then a boost of hot water goes into the system. The problem is that you are set for 5 - high mass setting. That is perfect for concrete but the boost of hot water will send in 165 plus degree water into the system which is not good for concrete.

WcIAfarmshop · 7:11AM

I have the boost turned off so the maximum temp is 119 in the boiler. Haven't had over 90 going into the manifolds so far.

Enough boiler ?

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