Radiant heat water temp reset?

ottostingray

I have a condominium building that we service. They have two old Bryan Flex Tube atmospheric boilers. One smaller for summertime use that heats a shell & tube domestic water heat exchanger. The other large boiler is 6,500,000 Btu beast that comes on when the heating season is here.
The heat is radiant floor heating in cement slabs. The apartments have no thermostats. The water temperature is controlled by old Honeywell W964 reset controls, two zones with constant circulation, each with its own pump, controller and series 90 mixing valve actuator. The obsolete W964 controllers are acting up and unreliable.
I want to replace them with T775R controllers. I an unsure what reset curve to apply for this situation. Right now the apartments are too hot and the tenants open the windows to cool off.
This is in Chicago. The building zones are north and south with north and south exposure. Windows are newer. The building is entirely concrete.
Eventually I would also like to get a reset control on the big boiler but for now, baby steps.
There is a 100% OA Make-up Air Unit for the corridors that uses a water coil on a mixing valve so I can not turn the boiler down so low that the coil does not get enough heat.

Thanks in advance for any suggestions or assistance

hot_rod

A lot working against you there. High mass, no individual unit temperature control, a large non modulating boiler, different tenant heat needs, yikes!
Might be nice to fine a Wi Fi control that you could tweak remotely, as it may take a few tries to find a happy medium.

ottostingray

Peakedtoosoon said:

Just to clarify.....
Two secondary mxing circuits, serving the north and south zones of the building?
All underfloor radiant heating?
The tenants have no local control of space temperature?
There is one 100% outdoor air unit for ventilation?
How many floors?
Do you know what the radiant design flow and return temperatures are?

Yes on the zones
Yes, all apartments are in floor radiant copper in cement
No, tenants have no thermostats. Maybe in the future but not now.
Yes, the MAU on the ground floor has a fan coil heater for the room and the MAU has a hot water coil to maintain 70° air
25 floors
I do not know what the design return temp is. The building was constructed in the 1970's and those design factors have been long lost in the decades.

ottostingray

hot_rod said:

A lot working against you there. High mass, no individual unit temperature control, a large non modulating boiler, different tenant heat needs, yikes!
Might be nice to fine a Wi Fi control that you could tweak remotely, as it may take a few tries to find a happy medium.

Good idea but for now I just want to propose a modernization of the old Honeywell controllers

hot_rod

Tekmar and HBX are a couple popular choices, add the remote access later if you need.

https://hbxcontrols.com/cpu-0550.php

ottostingray

Interesting. I will look further into that. One thing is this is a mixed/low income co-op building that still has a lot of issues to overcome. I will be returning to check the pilots & burners. Replace the MAU filters and leave more filters for the maint crew to change. Replace the zone pumps J5 coupler sleeves and one looks to be out of alignment. Replace the broken actuator linkage on the MAY mix valve. They don't have the money for huge upgrades all at once. I will try to explain that the efficiency gains would pay for themselves. Those old atmospheric boilers with their 36" stacks dump enough heat to supply another building!

ottostingray

So is there a basic setting you would recommend to start with using a T775R?
Min temp at warm outdoors like 70° water at 70° and Max temp at design like 110° water at 0° ? with a night time setback of 5° ? All the info sounds great and I know it can be a bit of a crap shoot at times but I gotta start somewhere.

ottostingray

@ Peakedtoosoon The building is 25 stories all concrete. Just looking for a starting point. It controls by mix valve discharge temp.

ottostingray

Zone sensors are a nice idea but it's not going to happen

hot_rod

ottostingray said:

So is there a basic setting you would recommend to start with using a T775R?
Min temp at warm outdoors like 70° water at 70° and Max temp at design like 110° water at 0° ? with a night time setback of 5° ? All the info sounds great and I know it can be a bit of a crap shoot at times but I gotta start somewhere.

Usually 68- 70F is a starting point, the high temperature if it is slab radiant? may be 110- 115. Floor covering makes a difference, if carpet is over the slab, SWT may need to be higher.

Without any design, maybe start with the settings that are currently dialed into the HW?

With the HBX or tekmar, you have room to grow the control system, if zoning is added or you want online capability. Wireless zoning is another option down the road. Start with the basic control, add as $$ allows.

ottostingray

Thank you

ottostingray

A bit of looking into the existing controller. I will try the 2.5:1 reset ratio with the recommended -25 Parallel shift. That will give me a 55° water temp at 70° and a 2.5:1 rise.
Thanks for he advice. I will look into the HBX. If we're going to upgrade, we might as well have options for future add on control. It all comes down to their budget and my sales skills.

ottostingray

Here's the manual for the old controller

hot_rod

ottostingray said:

A bit of looking into the existing controller. I will try the 2.5:1 reset ratio with the recommended -25 Parallel shift. That will give me a 55° water temp at 70° and a 2.5:1 rise.
Thanks for he advice. I will look into the HBX. If we're going to upgrade, we might as well have options for future add on control. It all comes down to their budget and my sales skills.

So on a 0 day you sent 175 to the slab? That seems awful high. 1- 1.5 seems more in. Line with slab reset.

pecmsg

ottostingray said:

Zone sensors are a nice idea but it's not going to happen

WHY?

ottostingray

pecmsg said:

Zone sensors are a nice idea but it's not going to happen

WHY?

They usually have a very limited budget. Running cable to apartment sensors would be expensive.

hot_rod

I think at some point the discussion with building owners with buildings like that is $$. If you want to go that far with them? I'd get past fuel bills and show them where zoning could save some big fuel consumption costs, and increase tenant comfort.

As fuel costs continue to rise, the concept of building upgrades, heating system upgrades makes more and more sense.