In-Floor Heating for a Shop & Greenhouse - Considerations ?

[dstig1]

Why do you think that increasing the flow will make much difference to the heat in the house?
Have you done some tests? There isn't much of a temperature differential between the concrete next to a heat tube and the fluid inside, so I wouldn't expect the heat to move into or thru the concrete very quickly.

My thinking is that if you are able to ncrease the flow rate through the piping, you will see the return flow will be warmer than before - and the concrete surface temperature will not change much.

rScotty

This is from my understanding of hydronic radiant heat. I see flow rates in the 5-6-7 gpm range for floors being typical. I have never been able to get mine above 3 gpm, and frankly 1.6-2 is much more common. This is pretty low for hydronic tubing as I understand it. And apparently increased flow leads to more heat transfer. I doubt we are approaching turbulent flow in any of these cases, as that would seem anathema to the circulating pump mode, but it is a key item that has vexed me.

QSF: You reminded me of another point from my history with this. My shop runs at 120F (and perfectly fine at that). The house started at 120F but due to the low flow I had issues getting enough heat so I eventually bumped it to 130. Everyone tells you to use numbers like 90F for a floor, so I was thinking I was already out of bounds at 120 and so 130 was nutzo, but it did improve output and worked a lot better. It did not occur to me that perhaps I could just bump it to 140 when it is really cold, so I will give that a shot this winter, when the time comes. So thanks for that memory jog and suggestion.

And while I get what you are trying to show with your example of air temps and output, I find things are never that 1:1 easy when it comes to concepts like heat transfer, but the direction you are pointing makes sense.

 

[quicksandfarmer]

This is from my understanding of hydronic radiant heat. I see flow rates in the 5-6-7 gpm range for floors being typical. I have never been able to get mine above 3 gpm, and frankly 1.6-2 is much more common. This is pretty low for hydronic tubing as I understand it. And apparently increased flow leads to more heat transfer. I doubt we are approaching turbulent flow in any of these cases, as that would seem anathema to the circulating pump mode, but it is a key item that has vexed me.

QSF: You reminded me of another point from my history with this. My shop runs at 120F (and perfectly fine at that). The house started at 120F but due to the low flow I had issues getting enough heat so I eventually bumped it to 130. Everyone tells you to use numbers like 90F for a floor, so I was thinking I was already out of bounds at 120 and so 130 was nutzo, but it did improve output and worked a lot better. It did not occur to me that perhaps I could just bump it to 140 when it is really cold, so I will give that a shot this winter, when the time comes. So thanks for that memory jog and suggestion.

And while I get what you are trying to show with your example of air temps and output, I find things are never that 1:1 easy when it comes to concepts like heat transfer, but the direction you are pointing makes sense.

There's a saying: all models are wrong, some are useful.

Do you see that you get diminishing returns from increasing the flow rate? That if you're at a rate where the water leaves at 120F and comes back at 110F, if you increase the flow rate you might get it coming back at 115F, and your average temperature goes from 115F to 117.5F. That's a pretty small increase. And if what you need is 130F water and what you have is 120F water, you're never going to get what you need with flow increases.

There's a reason outdoor resets are popular, it's easier to modulate the heat output of the floor by adjusting the temperature than by adjusting the flow.

 

[hoozie]

If and when we get to the point of building a big shop, I'm going to take a good look at a geothermal heat pump system. Preferably with a ground loop, but even an outside air unit can be used to heat water to go into the slab.

Operating cost should be lower than any fossil fuel, and even less if you have solar.

Something like this:

 

[quicksandfarmer]

QSF: You reminded me of another point from my history with this. My shop runs at 120F (and perfectly fine at that). The house started at 120F but due to the low flow I had issues getting enough heat so I eventually bumped it to 130. Everyone tells you to use numbers like 90F for a floor, so I was thinking I was already out of bounds at 120 and so 130 was nutzo, but it did improve output and worked a lot better. It did not occur to me that perhaps I could just bump it to 140 when it is really cold, so I will give that a shot this winter, when the time comes. So thanks for that memory jog and suggestion.

And while I get what you are trying to show with your example of air temps and output, I find things are never that 1:1 easy when it comes to concepts like heat transfer, but the direction you are pointing makes sense.

If you have an existing installation, and can measure its behavior, the modeling works well. Where it is pretty useless is trying to predict the behavior of an installation before it's built. That's the big Achilles heel of floor heat, each one is hand built and there are too many variables in how they get installed.

You're not going to break anything by turning the water temperature up. You may find it makes spots on the floor uncomfortably warm, that's a judgment call. The whole point of heating is comfort.

 

[quicksandfarmer]

If and when we get to the point of building a big shop, I'm going to take a good look at a geothermal heat pump system. Preferably with a ground loop, but even an outside air unit can be used to heat water to go into the slab.

Operating cost should be lower than any fossil fuel, and even less if you have solar.

I have an air-to-water heat pump on my house. It's a "developing" technology, I'd say you'd have to be somewhere between a tinkerer and a mad scientist to live with one. It works well with in-floor heat and fan units.

The manufacturer claims it exceeds the Energy Star efficiency standards for geothermal heat pumps. That's a roundabout way of saying it's supposed to be more efficient than a geothermal heat pump. Air source heat pumps have made dramatic strides in efficiency in the past ten years, and they continue to develop quickly. Geothermal is such a niche that they're not able to develop as quickly and take advantage of the latest technology.

Geothermal does have the advantage that the outside temperature doesn't affect performance -- when properly installed, which is a big "if." Air source heat pumps lose capacity as the outside temperature drops. I find around 10F is where my heat pump stops being able to keep up by itself and the supplemental heat kicks on.

 

[quicksandfarmer]

This is from my understanding of hydronic radiant heat. I see flow rates in the 5-6-7 gpm range for floors being typical. I have never been able to get mine above 3 gpm, and frankly 1.6-2 is much more common. This is pretty low for hydronic tubing as I understand it. And apparently increased flow leads to more heat transfer. I doubt we are approaching turbulent flow in any of these cases, as that would seem anathema to the circulating pump mode, but it is a key item that has vexed me.

QSF: You reminded me of another point from my history with this. My shop runs at 120F (and perfectly fine at that). The house started at 120F but due to the low flow I had issues getting enough heat so I eventually bumped it to 130. Everyone tells you to use numbers like 90F for a floor, so I was thinking I was already out of bounds at 120 and so 130 was nutzo, but it did improve output and worked a lot better. It did not occur to me that perhaps I could just bump it to 140 when it is really cold, so I will give that a shot this winter, when the time comes. So thanks for that memory jog and suggestion.

And while I get what you are trying to show with your example of air temps and output, I find things are never that 1:1 easy when it comes to concepts like heat transfer, but the direction you are pointing makes sense.

Just out of curiosity, how are you measuring the flow?

 

[dstig1]

Just out of curiosity, how are you measuring the flow?

One of the advantages of having an on-demand water heater is that it has a display for incoming water temp, outgoing water temp and flow rate... The manifold also has flow meters on it, but my flow is generally too low to get decent readings from that.

There's a saying: all models are wrong, some are useful.

Do you see that you get diminishing returns from increasing the flow rate? That if you're at a rate where the water leaves at 120F and comes back at 110F, if you increase the flow rate you might get it coming back at 115F, and your average temperature goes from 115F to 117.5F. That's a pretty small increase. And if what you need is 130F water and what you have is 120F water, you're never going to get what you need with flow increases.

There's a reason outdoor resets are popular, it's easier to modulate the heat output of the floor by adjusting the temperature than by adjusting the flow.

Yes, one of my favorite sayings. After I showed our young engineer how bad certain FEA models can get vs reality, I said, now lets talk about your obsession with climate change models which are far more complex and less developed...

As to flow rates, there is really nothing much I can do. Each zone has a Grundfos circulating pump and I added a larger Grundfoss to the main line as a booster to add more flow but it did not help a ton, as previously noted.

If you have an existing installation, and can measure its behavior, the modeling works well. Where it is pretty useless is trying to predict the behavior of an installation before it's built. That's the big Achilles heel of floor heat, each one is hand built and there are too many variables in how they get installed.

You're not going to break anything by turning the water temperature up. You may find it makes spots on the floor uncomfortably warm, that's a judgment call. The whole point of heating is comfort.

I used one of the online services (Radiantfloors.com or similar) to lay out the systems, so I am confident it is designed OK as far as the loop basics. All zones use 290-300' of tubing so are well balanced. I bought stuff from them for the shop and bought the tubing for the house from them too, but the rest of their hardware did not make as much sense for the house so I went rogue on that.

We don't have hot spots at all. So yes, I could try turning it up easy enough. Keep in mind, I already knew I was outside the bounds of "normal system design" at 120 so going to 130 seemed crazy. Now that I have the idea that it is not so crazy, and you need to do what you need to do, I can feel more at ease about turning it up more. I still haven't started the house floors yet for the year. We are supposed to have a warm snap next week and may hit 60, so probably another week for that to get fired up. Shop floor has been running for 2-3 weeks now, just fine as usual. Using the forced air furnace in the house currently.

I have an air-to-water heat pump on my house. It's a "developing" technology, I'd say you'd have to be somewhere between a tinkerer and a mad scientist to live with one. It works well with in-floor heat and fan units.

Caveat: depends on what climate you are in. In the mid south where heating is much less demanding, they probably work really nice. But do be advised that there is not terribly hot water coming out of a heat pump, so if you find like me that you need a higher temp, you are SOL...

 

[quicksandfarmer]

Caveat: depends on what climate you are in. In the mid south where heating is much less demanding, they probably work really nice. But do be advised that there is not terribly hot water coming out of a heat pump, so if you find like me that you need a higher temp, you are SOL...

I designed my system to use 95F water which is what maximizes output from the heat pump when it's cold outside. That gives me tile floors in the bathroom that are about 80F, everywhere else it's barely noticeable.

One of the nice things about the heat pump is that it has built-in outdoor reset, it automatically adjusts the water temperature based on the outdoor temperature. Right now it's 57F out and the water is at 86F, just enough to take the chill off.

 

[Williy]

My concern would be if you want to use you shop like in an hour
or half an hour you would have to turn on the heat the night before
because of the time frame to heat the room. If your going to leave it
on all the time no problem as the heat will be constant. Get your
self one of the kerosene blast heaters if you want quick heat.

willy

 

[Menagerie-Manor]

My concern would be if you want to use you shop like in an hour
or half an hour you would have to turn on the heat the night before
because of the time frame to heat the room. If your going to leave it
on all the time no problem as the heat will be constant. Get your
self one of the kerosene blast heaters if you want quick heat.

willy

I added a Hw unit heater to the system with valving for just that.