Old Radiant Hydronic Heating Control Issue

MasterC

Our heating system that I posted about years ago has been mostly working. But it should be able to regulate the subfloor temperature and does not (never has). I would like to fix that, if possible. I want to install some new vinyl plank flooring, but that requires keeping the subfloor surface temperature under 85 deg F. Right now it gets over 100 F.

The Question I am looking for help with is: what's the best / simplest way to use, modify, or add to what I currently have to get this to work like I want. This post is kinda long (sorry) because I tried to be thorough in describing what I have and what I know (or at least think I know).

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We have 6 in-floor radiant heating zones, and each of them is wired up like in the attached cartoon I made.



In short:

• A thermistor temperature sensor is located under the finished flooring.
  
• It is wired into a Goldline SP-30 Set Point controller through the heat control relay of a Ritetemp 8022 Thermostat on the wall.
  
• When the SP-30 output is ON, it closes a relay to apply 115 VAC to the Grundfos Zone Circulator, which moves the hot water through the loop.
  
• I think the idea was:
  • 8022 thermostat closes its relay when the room needs heat
    
  • that connects the thermistor across the sensor input terminals of the SP-30 (terminals 3 & 4)
    
  • if the thermistor temperature reading is less than the control setpoint, the output is on to drive the zone circulator pump
    
  • This would cycle the circulator in order to allow the floor to be maintained at the desired temperature continuously until the thermostat no longer calls for heat.
    

Sounds ok in theory, but...

Issue 1 - the configuration jumper settings for the SP-30s were all wrong:

• It was set up for External setpoint control, but there is no external set point controller connected.
  
• It was set for Cool Mode control, but this is for heating only.
  
• Somehow this actually worked to allow the control output to be on (running the circulator) whenever the thermostat called for heat, but the thermistor reading and SP-30 set point setting were completely ignored. This worked to warm the room, but at a completely unregulated floor temperature.
  

Solution (almost):
As I tried to change this configuration to allow regulation of the floor temperature based on the thermistor feedback, I changed the SP-30 configuration jumper settings to use Internal Set Point Control and Heat Mode. This almost works. For some of the zones, it actually does work as intended, but for others, it does not.

Issue 2 - behavior of "open circuit" across SP-30 sensor input terminals is not reliable:

• When the thermostat is NOT calling for heat, there is nothing connected across SP-30 terminals 3 and 4 (open circuit).
  
• This (usually) is interpreted by the SP-30 as a "sensor error" condition (I can tell because the Power Light is blinking).
  
• Sometimes that open circuit sensor error condition results in the SP-30 Control Output being off. If that were always reliably the case, we'd be good to go.
  
• Unfortunately, some of the SP-30 controllers don't see it as a sensor error and they turn the Control output on no matter what the set point setting is, and/or sometimes they do see it as a sensor error but still turn the Control output ON no matter what the set point setting is.
  

My theory is: this is happening because

• a) this is a use case for the SP-30 that it was not designed for, so the behavior during an open circuit sensor error is erratic, and/or
  
• b) thermistor resistance goes higher as temperature goes colder...so an open circuit looks like a really high resistance == a really cold temperature reading.
  

(Part b of my theory is supported by an observation that if I change the "Heat Mode" jumper to "Cool Mode" it turns the Control output off no matter what the set point setting is)

hot_rod

Can you just limit the temperature from the boiler? Not to exceed 90F for example 
That covers all the zones.

There should be no need to exceed 80-72 on the floor surface

If the system was under designed then higher temperatures are often the way to increase output.But floor covering and foot comfort take the hit.

MasterC

hot_rod said:

Can you just limit the temperature from the boiler? Not to exceed 90F for example 
That covers all the zones.

I think the only way to limit the temperature to the zones is by moving the lever on the Tekmar 4 way mixing valve. I also think if I limit the fluid temperature, I will not get adequate heating. I have tried running it at a lower setting in the past, but then on colder winter days it can't keep up.

Based on design info that came with the house, it looks like it was designed for a recommended fluid temperature of 130 F. The floors don't feel hot or uncomfortable to walk on...but I took some temp readings after peeling back the carpet, and the subfloor was over 100 F.

hot_rod

It depends on where you read the temperature. If you are reading right on top if a tube, compared to the mid point between tubes

Ideally the tekmar 4 way would have an actuator and constantly adjust the supply to the load.

SummitMechanic

An automatic actuator on the 4way valve will probably be the best and cheapest option just off the top of my head, but i would need to see more of the boiler room to confirm.

EdTheHeaterMan

It appears to me that the system is "under-designed" as Bob put it. If it works fine when you limit the water temperature from the boiler, then it is designed properly. If you have problems keeping up when it gets closer to design temperature (the coldest days), then you will need to increase the water temperature.

If you have new flooring that requires 85°F max floor temperature, then you will be stuck with less heat output from the floor.

If you need hotter water when it's really cold, but you can't use hotter water because of the new floor, then you are in a "Catch 22" situation. Lower temperature water can not make more heat because you need it to. Lower temperature water will yield as much heat as that temperature water will offer. No more, no less.

You need to re-think your floor covering or you need to add auxiliary heat to the problem room(s).

hot_rod

Or lower the thermostat setting 😗
Floor output goes up as ambient temperature is lowered

MasterC

Thanks for the help! I do think we have jumped forward past my initial question though, which in a nutshell is this: I have temperature sensors in the floors, which are currently not actually doing anything to control the system; how do I modify things to use them?

Once we get that figured out, I'd like to circle back and discuss things like an actuator in the 4 way and other potential improvements.

hot_rod

In a home it would be tough to use just floor sensors to control the system. You will have room temperature under and over-shoots. Solar gains, occupancy loads, rooms with different heat load needs, etc.

The radiant specific thermostats use both air sensing and floor sensing to best control the output.
So the sensor in the floor could be a high or low limit, but air or room temperature is the main signal for comfort.
If you have floor covering concerns the floor sensor becomes a not to exceed limit. But the room may or may not reach temperature based on just floor surface temperature input.

MasterC

Thanks @hot_rod ... what you described is exactly what I am trying to do - use the room thermostat for each zone as the main control for the room temperature, but with the floor temperature regulated to a set limit.

Rich_49

MasterC said:

hot_rod said:

Can you just limit the temperature from the boiler? Not to exceed 90F for example 
That covers all the zones.

I think the only way to limit the temperature to the zones is by moving the lever on the Tekmar 4 way mixing valve. I also think if I limit the fluid temperature, I will not get adequate heating. I have tried running it at a lower setting in the past, but then on colder winter days it can't keep up.

Based on design info that came with the house, it looks like it was designed for a recommended fluid temperature of 130 F. The floors don't feel hot or uncomfortable to walk on...but I took some temp readings after peeling back the carpet, and the subfloor was over 100 F.

The sub floor was over a 100* because it was beneath carpet , almost certainly . Take the floor surface temp in the same room not under carpet and see what that temp is .

MasterC

You may be right @Rich_49 - I will certainly try that out. Trying to wait for colder weather before I fire it up to do that, though.

In the meantime, I want to see if I can make some use of the floor temp sensor as a limit. Anyone have ideas on how to do that with what I've got? (Edit: Or with not quite what I've got, if there's a solution that would involve swapping out the thermostat for a different thermostat, or swapping out the SP-30 controller for some other device).

hot_rod

This is a better solution compared to that analog Goldline. All the control is in one location, easy to program.
It has more adjustability, digital readout, etc.
Download the application sheet to see how it works.

MasterC

Thanks for the suggestion! That Tekmar 519 looks like exactly what I wish they would have done when they designed this.

But as it is, I see a couple issues with that one. First, I have ~115VAC coming into the SP-30, not 24V. I probably could convert that with a transformer if needed. Edit: also, I only have 2 wires to my wall thermostat.

BUT the biggest issue is the 519 wants the floor sensor wired to the thermostat location on the wall, which I do not have. Currently my thermostat wires and my floor sensor wires both come to the boiler room, and I don't see a good way to wire the floor sensor directly to the thermostat instead.


Any other ideas?

MasterC

A little spendier, but it looks like maybe something like the Tekmar 564 might work? (I'd still need to get 24VAC power to it though.) At least I think it looks like I could install the "HVAC Interface Module" in the boiler room and wire my floor temperature sensor into it, and replace my thermostat with this one and connect just the 2 wires to the interface module.
(Edit: 1 issue is that currently the SP-30 controls my circulator pumps by switching the 115VAC through its relay, and the 564 uses 30VAC; so, I would probably need an external relay box as well to turn on the pump power.)

I could do that for the one zone I'm mainly worried about right now for the floor temp control... Ideally I'd have it for all the zones, but not sure I want to buy and install 6 of these. Some sort of multi-zone solution that does a similar function to this, but for multiple thermostats and temp sensors, would be nice, if that exists.

Teemok

Sp30 blinking light is anti-cycling lockout. Some of the sp30's might have sticking relays. It sounds like the designer/installer didn't complete and prove their design vision. A better use of the sp30 would be to make them open the 24v W wire circuit in the thermostat wiring when connected to an SR relay zone control switching the zone pump. The sp30 could use 24v ac supplied by the SR type relay (safer low voltage) or just keep it 120v powered while switching low voltage. Logic: If floor temp is below the limit the sp30's relay at rest with the normally closed terminals connecting the T-stat's W wire circuit with the SR type control relay. If the floor temp. goes above the limit the SP30 activates its relay opening the n/c switch disabling the t-stat call to the SR relay.

By the way, lots of flooring in full sun can be way above 85F for many hours. Some of this is imagined need for flooring product temperature protection and some is trying to idiot proof a complicated thing. It's a lot of CYA and blame avoidance. So many ways to do it poorly and a few to do it well.

This was stated well in a post above but I'll try to say it another way at risk of being repetitive. Limiting surface temps via a thermostat tied to the floor mass can put a zone into a "stall", to use an airplane term. Comfort is lift. If the space needs the heat due to structure heat loss while the floor is above the cut out high limit, it will get cool and colder in the space. It can take a while for the floor mass to drop and allow it to heat again. This cycles form depends partly on how the control was set up or not set up at all. It can cool so much that it takes a while to re reach the floor limit. The poor performance cycle repeats but the floor is always under the lawyers temperature limits. Enter the must have 70'S shag area rug placement drama, or the like, making it all the much worse. All that stall and recovery time is what I call uncomfortable minutes. Air conditions change fast. External inputs can change fast but the floors have a thermal inertia. They take time to respond and can and do over shoot. Too cold then too hot. Confronted with complaints a well meaning tech turns up the water temp causing more frequent stalls and bigger overshoots, more uncomfortable minutes. The floor sensor should be thought of as fail safe protecting the flooring from other components failure modes, not as a component in the space temperature control skeem. Expensive hardwoods over high output areas that are compensating for glass wall heat loss might be worth the effort to protect like this. Supply water temperature control with a good outdoor reset setup is best practice. I've worked on some motorized 4 way mixer systems that were very good. If there's a need to turn up the water temperature to floor killing temps to adequately heat the space, floor temp limiting should be seen as a performance compromising mitigation as well as flooring product protection.

Teemok

I see there's a blinking led for sensor error too.

Teemok

Taco SR506 is $280. Rewire pumps to it and use existing t-stats and your the sp30's and sensors as emergency limits. Not sure if all the devices are in one spot or if you have easy access to the sensor wires and thermostat R and W wires. Cross sells a $28 dollar box knock out 24v cube relay. Just need a 24v transformer and you could do only the problem zone. What triggers your boiler to fire?

MasterC

@Teemok
Thanks for your input! I have been off doing other things for about a month and did not see your posts...thanks so much for weighing in.

Teemok said:

By the way, lots of flooring in full sun can be way above 85F for many hours. Some of this is imagined need for flooring product temperature protection and some is trying to idiot proof a complicated thing. It's a lot of CYA and blame avoidance. So many ways to do it poorly and a few to do it well.

Am I interpreting correctly that by this you mean it could end up being just fine, despite what the flooring spec says?

Teemok said:

A better use of the sp30 would be to make them open the 24v W wire circuit in the thermostat wiring when connected to an SR relay zone control switching the zone pump. The sp30 could use 24v ac supplied by the SR type relay (safer low voltage) or just keep it 120v powered while switching low voltage. Logic: If floor temp is below the limit the sp30's relay at rest with the normally closed terminals connecting the T-stat's W wire circuit with the SR type control relay. If the floor temp. goes above the limit the SP30 activates its relay opening the n/c switch disabling the t-stat call to the SR relay.
...
Taco SR506 is $280. Rewire pumps to it and use existing t-stats and your the sp30's and sensors as emergency limits. Not sure if all the devices are in one spot or if you have easy access to the sensor wires and thermostat R and W wires.

I think you are onto something here...but I could use a little help understanding how to change the wiring from what I have to what you are suggesting. Right now I don't think I have a 24V W wire from my T-stats.
I mean, I have a W wire from each T-stat, but they appear to be only switching the floor sensor connections to the SP-30 rather than a voltage. Looking at the diagram in my original post, would I basically:
1 - disconnect the junction of the red wire and the floor sensor and then
2 - get 24V from somewhere to connected to the red wire?
3 - Then just hook the floor sensor wires directly to the SP30, and
4 - Take the W wire from the thermostat and connect it through the SP30's NC relay into a zone of a newly acquired SR506? And re-wire the circulators to be controlled by the 506 instead of the SP30.

I need to look more into how the 506 works.

I do have access to these wires all in the boiler room. You can see in these photos the column of red circulators on the one wall and the row of white SP-30s on the other wall.

MasterC

Teemok said:

What triggers your boiler to fire?

Forgot to answer this in my previous. I'm not certain what does it, but the behavior appears to be that the boiler fires when the water temp in its loop drops below a certain temp, and then it turns off after the water reaches a certain temp. I'm unclear on whether it is smart enough to also require at least one heat zone (or the DWH zone) to be calling for heat at the same time, or if it's solely based on the water temp coming out of the boiler.

Teemok

It sounds like you have the concept. DHW generation and priority is another complication but it's not that hard. How does the boiler heat DHW? Most boilers turn off completely when no zones are calling for heat. Some are turned with a seasonal switch and stay hot all the time turning on and off between their operating limits. Say 160F to 180F. SR506 relays are straight foreword. They have an isolated end switch "XX" that is meant to close the TT terminals of the boiler controller when ever a zone calls. Assuming you make DHW with a pump to an indirect tank you may already have a priority method in place or not. T.B.D. How the boiler is triggered now needs to be determined to know if the XX terminals of the SR506 will trigger the boiler or not.

Teemok

Depending on system age and plans for future upgrades it might make sense to have a motor operate the 4 way mixing valve that is outdoor reset controlled. This would making your floor supply water temperatures proportional how cold it is outside. If the reset is done right the sp-30's would never need to operate and temperature swings in the home would be smaller making it more comfortable.