Constatnt circulation radiant control

NYplumber

Hey there fellow HH members, summer is here and the radiant projects can be explored, installed, experimented. I have a short quick question on how you would control a constant circulation radiant floor (kitchen/bathrooms).



Indoor temperature feedback is needed to keep the room at a constant comfortable set temperature.



My approach that I see cost efficient using a buffer tank and a mod/con would be to use a Tekmar motorized mixing valve in conjunction with a radiant thermostat.





How would you do it?

Greg Maxwell

Constant Circulation

Constant circulation of modulated water is good in theory, but you have to be careful. I would talk to Tekmar, thier new house control may do what you are looking for. The careful part would come in regarding floor type. Is it a slab? If so, you have to be careful not to overshoot your temp. That type of mass will keep giving off heat long after your control has modulated the water temp down. Thats why we started to use injection of modulated water, so you can shoot small amounts of water into the floor, and maintain an accurate room temp. Staple up up is not as fussy, but you still have to make sure you have accurate room sensors that can anticipate an overshoot before it happens. 

STEVEusaPA

I'm currently using/experimenting with

a Tekmar 374 at my house.  Does high temp, 2 injection mixing zones, a setpoint zone, DHW, both priority/non priority, and of course outdoor reset.  The injection mixing worked great last winter, once balanced.  And the temps were fine tuned with balancing valves on the manifolds.  You can program any zone for a design temp, min temp, max temp, and they will work off of separate reset curves. (except for the DHW).

Jean-David Beyer

Indoor and outdoor sensors.

I used to run my radiant slab with only a conventional indoor thermostat, and no reset of any kind. I got severe overshoot. I did not really know how to adjust my boiler, so I left it pretty much alone. The temperature of the water delivered to the floor was controlled by the aquastat in the boiler and some mysterious piping and manual valves. I would guess the water temperature to the floor was around 130F that I now know is too high.



When I replaced that with a mod-con with outdoor reset, I adjusted the reset curve so the circulator runs a lot of the time, sometimes 18 hours a day. That is controlled by a digital thermostat inside, and an outdoor sensor outside.This is enough, under my conditions, to keep the temperature inside to within one degree of the setpoint. Technically, the indoor thermostat is an indoor sensor, but I realize this is not what is usually meant by that.



With a properly running system with outdoor reset, under what conditions would you get overshoot with a radiant slab? It seems to me the only time this is likely is if the system was running at a constant supply temperature for a day or more, and the outdoor temperature rose suddenly. The supply water would drop, but it would take 4 to 12 hours (in my house) to make a significant change in the temperature of the slab. Furthermore, once it hit the setpoint, the circulator would shut off and lower the heat delivered to the slab even more.



Now what good would an indoor sensor do in this situation. It would not know any sooner that the heat load was going to drop; actually it would be later. I am not saying that an indoor sensor is useless; I am just saying it is no help in this particular situation.



Where it seems to me to make the most sense is to use indoor sensors where there are several zones in a house whose heat loads vary between one another as a function of external events, such as the sun moving to or from a wall with lots of glass, for example. There the outdoor temperature might not change, but the heat load on the zone exposed to the sun would drop as the sun hits it, and the indoor sensor would be the first to know. Even here, it might be too late with an on-grade concrete slab such as I have.



The best way, I think to control reset, if the on-line hourly weather reports were any good, would be to use those to supplement the outdoor sensor. That way I could get 8 hours warning to decrease the supply temperature before the heat load changed. The weather data I get are not good enough for that, though.

Greg Maxwell

Constant circ

JDB, regarding setpoint control, you will get large swings in slab temp, that will result in over/under heating, so a Tekmar House Control may be your best bet. With indoor feedback, your sensor will anticipate need before it actually occurs, but I still would be cautious on a large mass like a slab, as you said, it can take a long time to balance temp. You may also look at a control with idleing, that will make up for some of you time to bring the slab up to temp. We used to to a lot of those. I still believe that the best bet is injection.

Steveusa, I think you are right on. Radiant should = comfort, not a lot of over or under shoot to balance a room temp.

Greg Maxwell

Constant circ

JDB, regarding setpoint control, you will get large swings in slab temp, that will result in over/under heating, so a Tekmar House Control may be your best bet. With indoor feedback, your sensor will anticipate need before it actually occurs, but I still would be cautious on a large mass like a slab, as you said, it can take a long time to balance temp. You may also look at a control with idleing, that will make up for some of you time to bring the slab up to temp. We used to to a lot of those. I still believe that the best bet is injection.

Steveusa, I think you are right on. Radiant should = comfort, not a lot of over or under shoot to balance a room temp.

Jean-David Beyer

I do not understand why you say that.

"JDB, regarding setpoint control, you will get large swings in slab temp,

that will result in over/under heating, so a Tekmar House Control may

be your best bet."



My best bet for what? I have a modulating boiler with outdoor reset. While I do not know what my slab temperature is (though I have checked it sometimes with my IR thermometer), I know what the supply temperature of the water supplied is. Above 50F outside, the supply water temperature is 75F. At 14F (design temperature), the supply water is 112F and if it gets down to 6F outside (I have never seen it get that cold, though it gets below 10F for a few hours each winter), the supply water goes up to 120F. I am  not sure what a Tekmar House Control would do for me that the outdoor reset on my boiler that modulates the firing rate of the boiler does not do already.



"With indoor feedback, your sensor will anticipate need before it actually occurs,"



It seems to me that, for my house at least, the outdoor feedback will anticipate the heat load change long before the indoor temperature begins to change, so it anticipates the need probably hours before an indoor sensor could do it. I have trees, small windows, etc., so the changes in insolation make less difference in my house than those of different design.



"You may also look at a control with idleing, that will make up for some of you time to bring the slab up to temp."



I do not know what that is.



"I still believe that the best bet is injection."



Why would that be so with a mod-con boiler with outdoor reset? The boiler can follow the outdoor reset curve and produce the hot water at the temperature required. There is no need to produce water that is too hot and then mix it down with an electically controlled mixing valve connected to either an outdoor or indoor temperature sensor. What would be the advantage of an injection system over a boiler that produces the water at the desired temperature?

Greg Maxwell

Slab Temp

If you can run a slab at the proper temp without over-riding with outdoor reset alone, thats great. I've seen a lot of systems overshoot using constant circulation. Also, it is seldom that you will have the same load throuout your house. How do you account for solar gain? Different floor coverings? Your outdoor sensor is theoretically on the north side where there is no solar influence. That, in my opinion only gives you a starting point, to run the boiler at. Your boiler curve should run slightly higher than your floor curve. Some zones may need an 85 degree floor temp while others may need a 75 degree temp on any given day. You cant compensate for that with a single temp system. While I do agree that constantly circulating modulated water would be great, its not feasable with multiple zoned homes to maintain proper comfort in all areas using one water temp.

CMadatMe

Indoor Reset

Take a look at the attached. Used is a few times and works like a champ.

Greg Maxwell

Hydonic Alternatives

I like it!

Jean-David Beyer

I must be lucky.

"If you can run a slab at the proper temp without over-riding with

outdoor reset alone, thats great. I've seen a lot of systems overshoot

using constant circulation."



I try to run at 18 hours/day circulation. And I get it sometimes. Usually it runs a little less. I have the outdoor reset curve set to get this; I do not have the circulator run all the time. I do this so that on extremely windy days that are very cold, the leakage of the house exceeds what the outdoor reset curve expects, and I just need to run the circulatoer a little more. And this happens automatically with just the on-off thermostat. So you could say that the thermostat overrides the reset curve sometimes. But it does it without my touching the thing. On very warm days, I could modulate even lower than 75F, but my boiler starts to cycle too much if I do that because it will not modulate low enough.



" Also, it is seldom that you will have the same load throuout your

house. How do you account for solar gain?"



I don't account for changing solar gain. My windows are double with argon gas in between and opti-coated. Furthermore, they are not terribly large and trees tend to block them. My kitchen has no door between it and the living room. One is on the east side of the house and the other on the west side. The outdoor sensor is on the north side. These compass directions are nominal, but wrong. The north side actually points somewhat west, so about 5 PM the setting sun will hit the outdoor sensor at a grazing angle. This does not seem to matter much as a practical matter. I balance the room temperatures with the valves going to the slab, so the two largest rooms with the greatest heat demand have their valves full on. The bedroom has its valve about 1/2 way closed, and the room with two large desktop computers has its valve almost closed. That is good enough  so I do not have thermostatic controls on those valves. Technically, the slab is all one zone. The load differs in each room because of the different sizes, number of windows, and heat load generated by the stuff in them. And that I have balanced out by setting those valves.



'Different floor coverings?

Your outdoor sensor is theoretically on the north side where there is no

solar influence. That, in my opinion only gives you a starting point,

to run the boiler at. Your boiler curve should run slightly higher than

your floor curve."



I am not sure what you mean here. What is my floor curve? I know what my reset curve is. I know what the temperature going into the floor (and the return) is. I would suppose these would be closely related. If you are saying that my floor temperature will be a little less than the supply water, this is obvious. So I imagine you are trying to say something else, and I am not understanding you.



"Some zones may need an 85 degree floor temp while

others may need a 75 degree temp on any given day. You cant compensate

for that with a single temp system."



It seems to compensate pretty well for me. My rooms hold +|- 1 degree all the time. Which I think is pretty good for in-slab radiant.



"While I do agree that constantly circulating modulated water would be

great, its not feasable with multiple zoned homes to maintain proper

comfort in all areas using one water temp."



It might work OK if the one water pump is a delta-P ECM powered one and the different zones are controlled by zone valves.



I wonder it mine works so well for me bacause the house is so small (1100 square feet Cape Cod). We have only been discussing my radiant zone, which is one zone. I also have baseboard upstairs that has a different reset curve. Upstairs has oversize baseboards so the supply there never exceeds 135F. Upstairs zone is very small and needs very little heat, say 5000 BTU/hour on fairly cold days.

NYplumber

Injection

Injection looks to be a more stable route for controlling temperature swings.



Jbd, I have read almost every post you wrote in the last long time. Not all have the luxury to fine tune their reset curve to what you have done since it would require repeated trips to customers homes, not to mention it would look unprofessional.

Inside feedback has many benefits.



HVHEHCC, which 3 way valves work with that control?



STEVEusaPA, the control is not cheap, but, radiant is a luxury and not a necessity. Which injection pumps are you using?



Greg, you are correct, inside temp sensor is the way to go when controlling solar gain.



For most jobs blending hot water to make up warm water is needed, therefore jbds approach doesn't apply to this thread.



Thanks all for replying.

Jean-David Beyer

it would look unprofessional

"jdb, I have read almost every post you wrote in the last long time. Not

all have the luxury to fine tune their reset curve to what you have done

since it would require repeated trips to customers homes, not to

mention it would look unprofessional."



I entirely agree. Not only might it look unprofessional, it would cost a fortune. And I do not have any idea how a professional contractor could explain to a customer why he had to charge so much for what looks so simple a job.  It took me a whole winter to get it set up. I mean I had no trouble heating the house with the factory defaults, but it got next to no benefit from the outdoor reset as it always supplied water much too hot. But if the outfit that installed that boiler came out 25x to fine tune that reset curve charged me their regular hourly rate, with a 1-hour minimum each time, the setup would cost almost as much as the boiler as listed on the Internet. Besides, they did not even believe in combustion testing, so I do not think they even knew how to set up the reset curves in the first place. To do that, you have to read the installation manual, and they seem phobic about things like that. It was trivial to do, since it just involves pusing the buttons on the front panel of the boiler, but if you do not know what you are doing, you will never get there. I mean it is not difficult, but it is boring and tries one's patience.



I first calculated the settings from my heat loss calculation. That might have been a slight improvement, but it sure showed that the approximations in the heat loss are too far off for this kind of thing (though it  OK for boiler siznig). The main reason it took so long is that I could not adjust the outside temperatures; I had to wait for nature to take its course. The trick is to get the supply temperature low enough that the indoor thermostat just fails to be satisfied, but high enough to heat the building. Of course, this cannot be perfectly done because the reset curve is a straight line (even though the manual says it is curved), and the load is not. Furthermore, the load changes slightly independent of the outdoor tempreature due to wind conditions, etc. I notice this primarily on very cold days with high winds. For me, hooking up a wind speed detector in connection with the outdoor thermistor might be the way to go, but I do not propose to do that. I am close enough for me.





"Inside feedback has many benefits."



I entirely agree. At one level, I have inside feedback: the on-off thermostat. But I realize you do not mean that. I agree that it would make a lot of sense for a different house or a different location from mine. A bigger house that really needed multiple zones on one floor, for example. Or a house that had lots of big windows not shaded by trees and maybe cathedral ceilings (solar gain issues). Or, in the case of a friend of mine, someone who operates a 12 KW pottery kiln from time to time. As I said, I seem to be lucky that my house is so simple to heat.



I have this funny, or maybe scary, idea of what happens when I die. Those reset curves (I have two zones with different reset curves) are set so I can heat the house to 69F. What if the new owner wants to heat the house to 72F? The boiler is about double the size it needs to be (smallest size in the product line), so the boiler would have no trouble doing that. But the resets are such that it would not do that. They would have to change the reset curves up a little. Depending on the contractor, they might even get a replacement boiler larger than the oversized one that is already in there. A pity. A friend inherits the house, but there is no way I can explain it to them. They have trouble hanging mirrors and changing washers in water faucets.

STEVEusaPA

re: NYplumber

Just the standard Taco 007, controlled by the tekmar.  On Tekmar's website they have an essay on injection pumping, how to size/pipe, etc. I followed it to a tee, especially the notes regarding spacing of tees, piping, etc.  Just don't forget the balancing valve in the return loop.   

Tekmar, great products, very hard to navigate website-even when you know what you're looking for.  Here's the link:

http://tekmarcontrols.com/media/literature/e0021_06.pdf

Let me know if you have any follow up questions.

CMadatMe

Diverting Valve

Its a diverting valve and can be purchased thru Hydronic alternatives with the control.

meplumber

Have you considered a floor temp sensor?

Just to throw out an idea.  Have you thought about using a floor sensor?

NYplumber

Floor vs Indoor

There are many ways to control radiant. Some use a simple on/off wall thermostat, some run constant circulation.

 

Im a fan of constant circulation, with the slight oversize of the floor output by either raising the water temp by a few degrees over design (selecting a more aggressive curve), and having indoor feedback in the event a sudden change of air temp, the room can catch up. In the event of a floor sensor, I dont see it recovering quick enough. Radiant is meant to be comfortable, however if the air temp stays cool due to the floor sensor (satisfied by the retained heat in the slab, gypcrete, mud-job) keeping the water temp at a constant temp while the window, door, etc was left open, the occupants wont be comfortable.

 Just my two cents, yet there are situations where floor sensor would shine. 

Mad Dog_2

I think floor sensor too, but I guess

Its too llate now.  Mad Dog