Constant Circulation radiant heating controls
New here, My Name is John.
Home is Fairbanks Alaska and I am designing a new home, I plan on using radiant floor heat with the tubing embedded in gypcrete.
I have done several projects with constant circulation in the past and have been happy with how well they perform it terms of comfort and temperature stability.
The PID control I have used in the past has been discontinued and looking for some options.
I will be using a oil fired low mass boiler with a buffer tank for the radiant heat.
Essentially the floor heat will pull tempered water from the tank to the two zones. One zone for the house and one zone for a apartment.
I do not require any boiler control or zone control.
The boiler has a manger that will control the temperature of the water in the tank.
The control I used in the past monitored room temp, and water temp at the 4 way mixing valve.
The mixing valve has a ESBE motorized actuator to control the water temp entering the floor.
This has worked well, however the actuator is noisy, and I have had to replace them and re-oring the mixing valve. Not a big deal and would do that again with a location further away form the occupants.
I would do this again if the control I used was still available.
I am aware there are other ways to do this, such as, variable speed injection and 3 way motorized valve.
Having no familiarity with those methods or controls I am looking for suggestions, the simpler the better.
Thanks.
Comments
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I prefer the Viega hydronic mixing block; simple & effective.
It controls constant circulation based on outdoor reset with an adjustable heating curve. No thermostat required.
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This is how I do CC on my shop. A basic 3 way zone valve. Normally open is B port to AB port, flow thru radiant. An Ecobee thermostat calls for heat, zone valve moves to A to AB, end switch calls on boiler. The boiler runs on outdoor reset.
I have a high temperature loop for doing product testing. I use a toggle switch to put the boiler in DHW mode, as a priority so radiant drop off when I'm running 180°
So basic off the shelf products but using all the boiler control features to fine tune. Step fire, ODR, and boost fuctions.
A Grundfos Alpha on speed 3 at 43W for a tight delta in the floor loops.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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Thanks for the replies, I am not a heating contarctor so bear with my lack of knowledge of some of these items.
The mechanical contractors here typically do not do constant circ.
The Viega mixing block appears to be very proprietary to me, I had a infloor unit years ago and started to have leaks and finally discarded it and went to a full flow Umpinor manifold. States it offers boiler control, which I do not need. Limited info on Viega website, will have to locate more info.
3 way zone valve, paticular brand? Ecobee tstat, which one? Is it a PID controller or just on/off for the zone valve.
I have used a 3 way Honeywell motorized valve and Johnson control for my shop, the input sensor to the control is insterted in a tube in the concrete, the Johnson control is slow reacting so the motorized valve isnt constantly chasing its tail. Works fine in a shop enviorment as temp flucations are not a issue.
At home the Paxton PID and 4 way valve are constantly making small adjustments to control water temp.
It works great and is almost heating nirvanna as the temp is always withih a few 1/2 degree (or less) of set point when I get home.
I apreciate the help and aplogize for some of the questions.
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Do you have a boiler in mind? Most all the mod cons have as much control logic as you could possible need, electronic stats can handle the rest.
You can add a slab sensor to most any electronic thermostat these days or use a hydronic thermostat like tekmar
But really constant circ systems don't need a lot of control complexity when used with a boiler controlled by outdoor reset. It will be a smooth even heating slab.I'm a proponent of tight tube spacing, maybe even 6" on center. This allows you to use the lowest possible water temperature. Solar, heat pumps efficient mod con operation, etc.
Maybe hire a local contractor to do a design for you, heat load, tube spacing, boiler and pump sizing, etc,
Rocky's Heating Service in Fairbanks is one of the best.Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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I thought I was the only nut that does tighter radiant tube spacing than the ..I've done 4" in some spots. Overkill? Maybe, but I've NEVER had a cold 🥶 spot on a floor. Mad Dog
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if you use 3/8" tube you can get below 6" spacing. I use that for bathroom tile floors for a nice even temperature. The old Heatway TwinTran was great for tight spacing and it was a counter flow design to even out the heat dispersion.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
I remember wanting to "stack" the Pex in a Hard to heat all glass twp story,, vestibule/portico to try to meet the tremendous heat loss, but The Slant Fin trainer, Jim Earhart (great guy..is he retired? Last I heard he worked for Watts) explained there was a point of diminishing return, i.e., you were going to put ONLY so many BTUs in to a given Sqaure foot of flooring.. We had to squeeze a small Sun-Rad on the Wall next to the door, actually did two to match..to supplement the Radiant . Mad
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I've heard the same, that going below 6" will not gain much output.
Tighter tube will spread heat better in a slab, a more consistenr flooe temperature across the room. We have both seen that. All slabs stripe a bit, tight tube minimizes that.
A chart showing tube space differances. And some IR
pics of 6 vs 12"
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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Since you are planning on using Oil with a buffer tank:
Tekmar Controls (Watts) makes controls that will ether modulate a 3 or 4 way mixing valve or inject on a primary/ secondary loop base on outdoor reset with PID function
BTW…Viessmann and Buderus have Plug and play with Modulating 3 or 4 way valves. You can combine this with none electric (TRV) Thermostatic Radiator Valves for easy total comfort.
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If you can use propane or natural gas a mod-con boiler is the only way to go with constant circulation. Let the mod-con do all the work. I would be concern that using oil if not done correctly the oil will short cycle a lot with the buffer tank.
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Thanks for the replies
My theory on tubing is you can never have too much but you sure as heck can have too little…..! I would use 1/2" in gypcrete today and 3/4" in concrete 3.5" or thicker.
I have used and would do a counterflow layout for tubing.
I know Rocky, hes a good Tech, but alwasy very busy.
Boiler will be a on demand System 2000 and I have no need for outdoor reset, essentially the zone control will think the buffer tank is the boiler and adjust flow or temp based purely on demand/set point. I would typically keep the temp in the buffer tank just hot enough so the boiler doesnt condense and cycle the zone valve to mantain tempertaure.
I have looked at Tekmar and am sure they have what I need, I was hoping to get some advice on a specific control, that would be great.
Slab sensor for the shop from my experience works great, for the house and apartment I think more precise control would be better.
Fairbanks winters can be pretty brutual in terms of temperatures, and the real key to comfort and efficiency is a well insulated building. One of my first jobs here was working for a contractor building double wall homes in the early 80's. I learned a lot and realize the benefits of "efficient" home.
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Natural gas is not a option and LP is expensive. I have used oil in the past and the key is the buffer tank, especially in a low mass boiler.
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Yes, run the buffer at a fixed temperature, pull the radiant off with ODR control. I've lost track of current tekmar #s, I'm sure they have a control to run a mix valve off ODR.
HBX is another good option for controls. Between tekmar and HBX I think they OEM to most every hydronic control module.
I've done training at the Cold Climate Housing Research labs a few times over the years. We supplied the solar thermal they have on the roof. Some pretty amazing low load buildings they have planted around the state.
I was involved with the Weller School project also. They have a solar thermal system that just dumps into the earth all summer to boost the heat pump efficiencies in the winter. I've forgotten the engineers name, they were datalogging that system. It would be interesting to know how well a geo heat pump works in that severe climate. It was 23 below on one of my visits up there. Permafrost and geo loop fields, an interesting mix :)
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
Great comments all around. @Gardyloo , I'll PM you piping and wiring drawings using a simple Taco control. This can be modified for continuous circulation, but here's the basic operation: The thermostat call opens radiant zone valve. The endswitch (or thermostat in single zone) calls PC705-2 control. The radiant circulator and injection pump will start. The PC705-2 Control varies the Injection Pump speed to provide the desired supply temp. The Buffer Tank aquastat is wired in series with warm weather shutdown relay RIB2421C (N/O contacts) and to T4 and A1 on System 2000 manager, providing a call for heat.
Best,
Roger
President
Energy Kinetics, Inc.0 -
Sometimes oil is the only realistic option. Sometimes it's a preference.
Sure the oil is on/off bur with a buffer tank at 160° and a 40° differential, then mixing at 110°- 115°, I don't see short cycles unless the boiler is oversized.
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ODR controls can get you close to constant circulation, but not 100% of the time, as when outdoor temperature is hit.
A circulator running all the time does provide constant circ. Many Euro systems run with delta P circs plugged into the wall running constantly. A heat call has the boiler turn on and provide BTU. Early German boilers that came to the US didn't even have TT connections!
One nice application for constant circ is a building with high solar gain, radiant slabs. The south facing slab grabs the solar gain and moves it to rooms that are not experiencing solar gain. It lessens over-heating in the south rooms and move some energy to rooms needing heat, without firing the boiler.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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I know the folks at CCHRC very well, more so when they first got started. Jack is a friend and apparently Bruno is running the show now.
The Weller school project is interesting. My impression from discussions with the school distirct people is the the uninsulated "earth field" will soak unlimied amounts of heat and it simply disapates into the 38 degree ground.
Some geo heat pumps are in use around here, there are some heady claims they work, however they are power intensive and I have written it off unless we get access to cheap power. I am looking at some solar collectors and storage ideas for the future. I will make some provisons during the building process to work this in later.
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I have wondered about running a higher temp in the buffer tank, my concerns would be if a control failed and 160 degree water entered the floor, assuming the controls deal with a 40 degree differential?
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Exactly right. That is the difference between heat and temperature. If you have 100 degree water, once the slab gets to 100 degrees, you could run the tubes side by side touching each other and no more heat gets transferred as you need a delta T for heat to move. Once you are much closer than 6”, the “cold” area between the tubes is so near in temp to the “hot” area above each tube, that another tube in between is only serving to displace concrete and will transfer almost no additional heat.Mad Dog_2 said:I remember wanting to "stack" the Pex in a Hard to heat all glass twp story,, vestibule/portico to try to meet the tremendous heat loss, but The Slant Fin trainer, Jim Earhart (great guy..is he retired? Last I heard he worked for Watts) explained there was a point of diminishing return, i.e., you were going to put ONLY so many BTUs in to a given Sqaure foot of flooring.. We had to squeeze a small Sun-Rad on the Wall next to the door, actually did two to match..to supplement the Radiant . Mad
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Tekmar has great products. Give them a call with your requirements. Support will point you in the choices you have. I’m thinking 402 might be what you could use. Check to be sure.
Best with your project.0 -
I always said a double-wall home would be the most efficient to heat. An air gap in between insulations on an outside wall. Yes, it would cost a little more to build, but the savings in fuel would far outweigh the extra cost of building.Gardyloo said:One of my first jobs here was working for a contractor building double wall homes in the early 80's. I learned a lot and realize the benefits of "efficient" home.
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Also in Alaska. Have tried several system methods, starting with Boiler pro recommended design.. After complexity induced weakness, now I choose simplicity.
Have
-Tubing is cheaper than aluminum fins, add more tubes, 6 in or tighter. Have not used gypcrete. Use plastic plumbers tape loop with screw and install under floor, it hangs a little below floor surface for greater width of heat via heat camera.
-3/8 tubing has same thickness as 1/2, so tube r-value to heat content is higher, was disappointed.
-Last system, used 3/4-3/4-1/2 tees to build manifold under the floor, with opposite feed and return for equal length path. So manifold built under floor. No leaks even after a tenant let it freeze. This worked really well.
Why, since all loops are parallel and short, flow is slow close to slug flow. Pump head is really low. No manifold assemblies in the boiler area, space efficient.
On NG, and run a high efficiency boiler, lower temps than an oil can run. I don't use a mixing valve. Boiler temp ranges from 110-140 at minus 20 outside.
In order to increase temp Delta, and heat two low grade other zones. I run some of the return water from the floor, through a garage slab, in tandem by adding as slight resistance to return water. It may sound crazy, but when the heat load goes up in the house, it does in the garage. So I don't need another valve.
DWH, as is usual, bonus points for a second DHW after the first as a preheater, better heat scavenging, reduces stratification of first tank with tempered water.
Have also setup a left over DHW tank 'backwards' FWIW. After floor heat, after garage floor heat, boiler water passes through a 30 gallon DHW tank before returning to the boiler. Why. Creates a thermal storage, and allows boiler to shut off, but still provides a low grade of heat to the floors. Second. I put a glycol loop in the coil for outdoor use. The glycol loop, uses the 'coldest' left over heat anytime there is a call for it, it doesn't call the boiler, it's not that important. I use it open drains in the spring to remove melt water freezing at night. Turn it on for day or two then off.
So one pump for house, garage and valved storage tank, 75 watts summer, 95 watts winter. No flow restrictive valve needed.
DHW, has a valve, DHW calls for heat, valve opens, boiler temp rises, most of the heat goes here. Valve closes, heat goes to house. If valve fails, I don't get hot water.0 -
Double walls do work, typically 2 X 4 spaced a foot apart and insulate with 6" batts, one downside is the studs could twist since they were only secured on one side, this was not a huge issue, but it did happen now and then. It does eat up some floor space. There are many ways to skin the cat. One of the current trends for super-insulated is the remote wall system, typically 2 X 4 framing and min of 6" of rigid foam on the outside, strapping and then siding. They have some advantages and work really well.JAdams said:
I always said a double-wall home would be the most efficient to heat. An air gap in between insulations on an outside wall. Yes, it would cost a little more to build, but the savings in fuel would far outweigh the extra cost of building.Gardyloo said:One of my first jobs here was working for a contractor building double wall homes in the early 80's. I learned a lot and realize the benefits of "efficient" home.
First they virtually stop all conduction through the framing members. Also they allow one to work on the inside and heat the building during the process, assume the foam is on. This is great in cold climate with short building season. Since the foam is applied to the exterior, no floor space is lost. However there are lot of details at the opening and particularly at the door thresholds. Applying the strapping with long screws is labor intensive. In general the process is labor intensive.
I plan to frame with 2 X 6, spray foam in the cavity, sheath the exterior and install 2" of rigid foam, then siding. Per square foot of wall it is slightly more expensive, but easier to execute. I suppose it will end up where the price of foam lands.
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Hi John. Nice to see a post from another Fairbanksan
I'm a heating contractor here, and I've had excellent results from utilizing a Tekmar control with indoor temperature feedback from their communicating thermostats. Outdoor reset provides a starting point for the supply temp curve, but the indoor feedback allows it to closely match BTU output to the demands of the room. In this way the supply temperature is lower than than outdoor reset alone. The system circulator runs almost continuously. I also echo 6" radiant tube spacing, and also not at the bottom of the slab. I'm happy to discuss this with you in person. Feel free to send me a message. 1 -
Is it ok to use the Heat Pump water heaters for this kind of set up? From what I've been researching, they are far more cost effective long term. Anyone have experience using these for in floor heating? How much square footage does something like this manage?0
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@bmoon , heat pumps "move" heat. Heat pump water heaters get about 1/2 to 2/3 of their heat from the room and the balance is from the electricity it consumes. This means the room gets colder and the domestic water gets hotter, which is not a good strategy as a source for space heating in a cold climate like Fairbanks (unless there is some very substantial source of waste heat inside the building envelope).President
Energy Kinetics, Inc.
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John, we sell a Swedish brand of mixing valve motor/control all-in-one. It is called Smart Comfort. https://store.tarmusa.com/collections/mixing-valve-controllers1
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John,
You might also look at Taco's i-Series mixing valves. They can do outdoor reset on the mix from buffer tank into floor loops or maintain a set output temperature, depending on where you place the sensor and program the switches, without the need for a second injection pump.
https://www.tacocomfort.com/product/iseries-mixing-valves/
These do continually but quietly "search" for the best mix, so if that is objectionable this may not be your best choice. On the plus side the LED and knob (showing the ball valve position) give good feedback of what it is up to.
Gypcrete does not conduct heat as well as regular concrete, so bear that in mind when calculating radiant output. With the water temperature you have available from an oil boiler I can't imagine that would be a problem. I have never run into the limits of getting heat out of lightweight concrete, but then I am in North Carolina so rarely hit the limit on any heating system.
Tom WillsSol Brother0 -
Thanks for all the replies, will have to dig deeper, we have gotten busy at work and will look as I have time.0
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