Setup for radiant heat in concrete floor
Hi, new to your forum. Looking for some advice for most efficient setup for my heating system. I have a 1500 sq ft work shop with a 14 KW boiler with 6 loops of 1/2" tubing of 250 ft/loop. I maintain a temperature of 58 degrees, with a boiler setting of 120 degrees. I have operated this system for several years, and performs well. Just wondering if I can make adjustment to run more cost effective. Welcoming some input of boiler temp settings, pump speeds and mixing valve settings.
Thanks
Comments
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is this an electric boiler? If so, no, not really. You can always lower the temperature, but very marginal gains to be had with an electric boiler. The expensive fix would be using something more efficient - like an air to water heat pump.
If gas or oil, same deal. Not much efficiency to be had. Gas condensing boilers are more efficient but you’re already in the condensing range so if you have one, it can’t get much better.
Overall, lower temp is better and is free to change, so even if you save little, it’s better than nothing.
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Yes, an electric boiler. What temperature setting would you recommend? What about pump speed setting? low, med or high?
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An electric boiler is always 100% efficient, in the sense that all of the electricity that goes into it comes out as heat. A hydronic heating system is always 100% efficient, in that all of the heat that comes out of it goes into the space. There is no way to make it more efficient.
The only way to make it use less energy is to have it put out less heat. In other words, keep the space colder
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Just try lower temps. The worst thing that happens is you’ll have to raise it. Unfortunately, your costs are going to be about the same. There’s really not much to improve about the existing system.
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Two thoughts:
What kind of pump? Newer technology pumps use less electricity. Same electric use for the boiler though.
Does your electric utility offer Time Of Use rates. The concrete slab is a large thermal battery. You can heat it up overnight when rates are low, then coast through the day.
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Not sure if you can add a set back control to change the water temp to the system based on the outdoor temps. Tekmar has a few options…just not sure if they are high voltage set ups.
Or you could change fuels to a boiler that would do that….
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What make and model is this boiler? I'm not aware of any manufacturer that makes a 14kw unit in an actual boiler- only water heaters. If it is indeed a water heater such as a HydroSmart/Stiebel Eltron, there is quite a bit of energy to be saved by going to an actual boiler which pulses and modulates for the load. If the space is adequately insulated, there is also some to be gained by turning the supply temp down closer to 90* aside from possibly design conditions where it may need to be bumped slightly higher. If you are using a mixing valve at all, it should probably be removed altogether. Your circulator(s) may also be able to be turned down or swapped to something more energy efficient, but that will depend on your heating unit, piping, and fluid being used. There are a lot of variables in systems like this unfortunately- it's not as simple as "do this and it'll be perfect". Hydronics is very forgiving in that it doesn't take much to make something work, but making it work well is a whole different story.
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All of the "wasted" electricity from the pump is converted to heat which warms the space.
The only possible efficiency gain is if sometimes the space is heated more than you would like. In that case, you could save electricity and money with a different control mechanism that does a better job of regulating temperature. But if the space is being kept at the temperature you want, 100% of the electricity being consumed is going to heating the space.
If some of the heat is going to places other than the space you want heated, that's a potential savings too. For instance, you could insulate the walls better. The big issue would be whether there is insulation under the slab, but fixing that would require taking up the slab and putting down a new one, which is probably not feasible.
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All of the "wasted" electricity from the pump is converted to heat which warms the space.
Good point. If you were heating with gas, a new pump might save some money, but since you are heating with electric…
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Here is a picture of my setup.
I am not a fan of the term that electricity is 100% percent efficient. However true. Just because it's not wasting any energy, does not make it cost effective. That was what I was pitched when purchasing the electric boiler. And was talked out of a natural gas boiler. Now years into it, I discovered that gas would have been much cheaper on the check book. Not currently looking to change out the electric boiler, just hoping for some tips to get the most bang for the buck.
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"I am not a fan of the term that electricity is 100% percent efficient. However true. "
I really don't know how we can help you then.
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The advice is simple, if results may be underwhelming. Lower the water temp and save a few percent maybe. You will not see substantial savings without changing to a heat pump or another cheaper fuel.
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The more efficient system would have been during construction. How well the insulation is holding up under the slab and around the perimeter. If it was poorly insulated before the slab was poured, then there is nothing you can do to make it more efficient in the "radiator" or emitter part of the system.
Changing the rate of flow thru the tubing will have very little effect on the temperature of the slab.
The only other thing I can think of is how well the structure is insulated and sealed. Adding attic Insulation or ceiling insulation and wall insulation will lower the amount of heat that escapes the structure’s envelope. The whole idea is based on the temperature difference between the outdoor temperature and the indoor temperature, and how fast the barrier between those two places allows the heat to move past it.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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If the thermostat set point is kept the same, lowering the water temperature just means the pump will run longer and the electricity usage will be the same. The only thing that will reduce energy usage is to lower the thermostat set point.
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@Hot_water_fan, Is underwhelming a word? I believe you can be overwhelmed, but I do not believe you can be underwhelmed or even, just whelmed, for that matter.
I can see the word Whelmed in the dictionary:
D1. (verb) not overwhelmed, not underwhelmed but whelmed just right.
Goldilocks was whelmed just right in baby bear's bed.
D2. (adjective). unaffected, unscathed, untarnished, understood.
The family of Bear's were whelmingly unaffected by the lack of power of the little girl sleeping.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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look into off peak rates, charge a buffer tank to reduce electricity costs if you have reduced rates available
Why is the valve between the close tees throttled?Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
As I had stated above, what you have is a Stiebel Eltron water heater that the Hydro Smart guy slapped a boiler sticker on. It is NOT a boiler. Your system circ is much bigger than it needs to be so you could save a few bucks a month by swapping it out to a 15 series like the primary loop or even an ECM unit, but aside from that and turning the water temp down, there is nothing to be gained without switching out your water heater for an actual boiler.
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Thanks for you inputs.
hot_rod, should I have the valve wide open? I had read something in the past about throttling the valve.
Ground up, I am surprised that what I have is not a boiler. It was advertised as one when I purchased it. Could you please explain the differences between a true boiler, and what I have? What boiler would you recommend? What power saving could be expected to upgrade to a proper boiler?
I was interested in an air to water heat pump. They appear to be quite spendy. Wondering how many years it would be to hit the break even point? My usual power bill for the years is $1500-$1600. Should also mention that I am located north of Winnipeg, in Manitoba. We do see some cold weather here. At what temp are these units generally ineffective? What BTU size would be needed?
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Can we just stop with turning the water temperature down? An electric water heater isn't going to have higher efficiency at lower temperatures, its efficiency is 100% at all temperatures.
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Yes the valve between the tees needs to be wide open. Pressure drop between the tees wants to be as low as possible.
Another advantage of the lowest possible operating temperature is you avoid overshooting the room temperature.
The outdoor reset controls this best, modulate the boiler temperature based on the changing load.
Basically changing the distribution efficiency a bit by modulating.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
For an approximation, a heat pump will use 2/3rds less electricity. So $1000 savings if all goes to heating. It can do cooling if that interests you.
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This article explains how to use your energy use history to size your equipment:
All of the air-to-water heat pumps I'm aware of have their output drop off pretty significantly when it gets cold, maybe half the output at -18C that they'd have at 5C. Do you know your design temp? If you were in the US I could look it up by zip code but I don't know how to get that for Canada.
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If you are considering an air to water heat pump, we have done some number crunching for you. One shows the COP changes, the other the output.
At -15C you could still be in the 2 COP range.
But a 5 ton, 60,000 btu/hr unit drops to about 20,000 at -15C.
typically on extreme cold days you could
have a LP or firewood supplement
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
Can we just stop with the ignorant comments? Nobody said anything about the combustion efficiency- it's largely irrelevant. Overall system efficiency of a unit modulating and running only warm enough to meet demand will be considerably higher than a wildly fluctuating and flywheeling thermal mass 99% of the heating season. It's not uncommon to gain 10-15% with a swap like this- I do several dozen per year swapping this Menards crap out with actual boilers from Electro Industries. If the OP decides to swap the boiler however, NG would still probably be the best route.
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Electric boiler efficiency would not change, system efficiency may with modulated or lower water temperature.
The downward loss decreases when the slab runs cooler for one thing, that could pick up % points.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
"But a 5 ton, 60,000 btu/hr unit drops to about 20,000 at -15C. Typically on extreme cold days you could have a LP or firewood supplement."
Most commonly with heat pumps you just do an electric resistive element for the supplement. Chiltrix makes an inline heater that uses a regular 5600W water heater element and goes on the heat pump output, if the water is below setpoint it comes on automatically and tops it up.
There's also a place on their buffer tanks to screw in a water heater element.
I don't know why the inline heater is 400 bucks though.
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There is an A2W heat pump company in Manitoba. Arctic. I have installed one on a well insulated small house in Vermont with a radiant slab and it also has a small Rinnai LP mod/con as back-up. It works great. It has a buffer tank.
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