Adding dhw priority to tekmar 261

SweatyInToronto

We have 2 boilers for space heating and a seperate water heater boiler with 2 storage tanks 100 gals each (edited for clarity) 3 gas burning appliances all mid eff currently.

Was recommended to us and I like the idea to get rid of hot water heater and replace with a heat exchanger utilizing the spare capacity of the boilers.

Our tekmar 261 doesn't have hot water priority, so is there a some way to add dhw priority and not lose the 261 functions or cause conflicts?

I was looking at the taco pc 702 as an alternative which has dhw priority but I'm not sure if we need another control with it. All we have is the hot water and a 2 stage boiler setup with one zone for heating. I've seen using zone controls in conjunction with it.

The tekmar 274 seems like it would work by itself without other controls but also $$$.

Our contractor is great but wants to get rid of 261 and just add relay for dhw but I'm concerned about losing features like boiler rotation, wwsd, outdoor reset, differential, etc. Maybe those are just marketing but I think they help to some degree.

What's your thinking and thanks for your input!

STEVEusaPA

Why not just add an indirect on its own zone, wire the indirect aquastat in the usual way!

SweatyInToronto

> @STEVEusaPA said:
> Why not just add an indirect on its own zone, wire the indirect aquastat in the usual way!

Thanks for your suggestion Steve.

Not really familiar with zones on the 261. Would it have priority in the winter, and would it split the demand? Is a separate zone control needed?

Ironman

Just adding a heat exchanger is not gonna work properly. How would you vary the boiler input to it as the demand fluctuates?

Use an indirect like Steve said and add a Taco SR503 before the Tekmar 261. Put the indirect as the priority zone in the SR503.

SweatyInToronto

So an indirect is basically a heat exchanger inside a storage tank correct? Maybe I should add that we have 2 100 gal storage tanks currently so the idea is to replace the external hot water heater with an external heat exchanger that has a seperate loop to the boilers through a splitter of some type (forget name) that handles pressure differences. Pumps control flow I believe.

The hw would have priority. Water temp goes up to 180 when its called. Back Down to 140 min for space heat.

Getting internal dwh tank maybe but much different? More $ probably. But I admit ignorance when it comes to deep understanding and terminology and experience!

Thanks... will try to understand!

Ironman

If you have storage like that, then yes, a properly sized and installed HX could work.

SweatyInToronto

Thanks Bob.

So then I guess it goes back to the original question about controls. What would be needed for dhw priority with the 261 if that's possible or alternatives mentioned?

hot_rod

Do you want a build your own solution? A RIB relay with double throw would work. Any time HW calls it drops power to the heat zones. That is basically what a priority call on relay boxes does.

Are you currently powering a single system pump from 7&8?

Need to see a bit of the piping to see where you would put the HX and how it would be pumped.

SweatyInToronto

Well Rod I'd say a brand name is fine too.
There is a single system pump. I'm not sure how it's wired but it runs continuously during the winter, I believe even during wwsd but not sure about that.

Would adding that relay or equivalent be wired Into the 261? It could tell the 261 to forget about space heating until dhw is hot enough and 261 wouldn't attempt to take back control if the radiator loop cools down below the differential?

In any event I'll try to represent they system better with a diagram of some sort. I know it's hard to answer without knowing the layout really well.

hot_rod

Basically break the power to the current system pump, then power goes to the HX pump, similar to this drawing but a heat exchanger for DHW, not snowmelt, of course.

So the tank aqua stat connects to the RIB, NC goes to P1, NO goes to the hX pump. The tank aquastat switches the RIB. The RIB choses which pump runs.

The RIB could either interrupt power to the 261 on 5&6, but your display goes out. Or interrupt 9break) #7 when dhw calls.

Unless you have enough boiler horsepower to run heating and DHW at the same time? You would need a building load calc, see how the boilers match up, give any additional output to DHW generation. With two boilers staged, it could be you have some additional BTU available?

20- 30 bucks buys a RIB relay, some wiring and a 4 square junction box or mount the RIB right onto the 261.

Kinda need to make both ends meet in the middle.

Ironman

@hot_rod
Wouldn't it also have to close # 3&4 "set point demand" to override the ODR for domestic heating?

SweatyInToronto

The boilers wouldnt have enough to meet dhw and space heat simultaneously for at least a part of the winter i guess. The building holds heat well but heavy hw demand could overwhelm on a cold day and we'd get complaints.

If wired as you suggest would the 261 still stage the boilers on a hot water call, rotate first start after 48 hours accumulated? Wanted both to be avail for hw even though one could be dedicated. Iike both for hw in case there is failure of one or the other. But want to avoid short cycling in the summer especially. Am I making it too complicated?

I mean initial cost wise there's not much savings doing the HX rather than another standalone dhw boiler. Id imagine there would be lower longterm costs maybe in gas and maintenance. How much hard to say....

Zman

What hot rod is describing would be a slick solution.
You may need a relay with a few more poles (or 2 relays) to make all this happen.

If you want to keep the WWSD feature on the 261 for heating, you will need to make the DHW call a setpoint demand on the 261 so it will override WWSD. It should be noted that the 261 will no longer turn on the boiler pump with a setpoint demand. https://s3.amazonaws.com/s3.supplyhouse.com/product_files/261-install.pdf

If you post a sketch of the proposed piping and existing wiring, this should be easy enough to map out.

The 261 is a simple and elegant little controller (unlike some tekmar products). Do not let anyone talk you out of it just because they don't understand how it works.

SweatyInToronto

9:49AM

>What hot rod is describing would be a slick solution.
You may need a relay with a few more poles (or 2 relays) to make all this happen.

AOK. A taco relay w dhw priority is fine even if a hundred or two. Not sure if the tech would want to go off label.

> If you want to keep the WWSD feature on the 261 for heating, you will need to make the DHW call a setpoint demand on the 261 so it will override WWSD. It should be noted that the 261 will no longer turn on the boiler pump with a setpoint.

I'm pretty sure the boiler pumps run even when it's not firing, and I'm not talking about post purge. They may not be wired in. They are small armstrongs.

Thought about the setpoint demand. That would act like a second zone. If the contractor put in the relay he wanted for dhw priority to those poles it would override the space heating settings but when setpoint call was complete, they would revert right?

> If you post a sketch of the proposed piping and existing wiring, this should be easy enough to map out.
>

Will do what I can. Photos may be safest!
Won't be able to get until next week.

> The 261 is a simple and elegant little controller (unlike some tekmar products). Do not let anyone talk you out of it just because they don't understand how it works

Thanks!

HVACNUT

Having a dedicated boiler to take care of 200 gallons of hot water isn't a bad idea.

SweatyInToronto

> @HVACNUT said:
> Having a dedicated boiler to take care of 200 gallons of hot water isn't a bad idea.

Yeah it's been that way a long time.
Its a 21 year old rbi spectrum 199k.
If it would keep going another 10 years till the boilers were 25 years old it might pay to keep.

Recently replaced the gas valve but am concerned about its heat exchanger and seals. It had a major leak for a week after replacing the circulation pump to the storage tanks. Was running a rivulet from both sides for that long and then seemed to fix itself. What a relief that was!

We can get a cheap replacement boiler and then replace all 3 mids with 2 larger high eff and indirect probably in 10 years. We can'tput in a high eff heater now due to venting issues and cost of overcoming them.

HVACNUT

Do the HX and replace the 261 with a control that has a priority override relay. I'm sure Tekmar, or someone has one. Maybe it was even mentioned ☝️up there. If you're going to do it, do it right. IMO, this is not a place for MacGyver. Your service tech will appreciate not having to wring out RIB splices at 3 a.m.
What did Jake say to Sister Mary Stigmata?

BTW, how old are the tanks?

SweatyInToronto

Recall tanks about 12 years maybe a few older.

The tm 274 is 261 plus dwh priority. The taco PC702 is similar. I'm trying to find out they are enuf or if anything else is needed from communication point of view. The 274 is about 1000 CAD;taco maybe half that but don't have quote yet.

Yeah would like to keep it pretty standard so anyone can understand and maintain it!

Would u think the HX approach is lower operating costs than separate mid eff dhw boilder? The startup costs would be 5-9% more for the HX with extra pump and electronics.

Zman

A couple relays would be $50 and would do the same job. If you are worried about the next tech figuring it out, just leave a wiring diagram and label the relay.

SweatyInToronto

> @Zman said:
> A couple relays would be $50 and would do the same job. If you are worried about the next tech figuring it out, just leave a wiring diagram and label the relay.

Thanks bit what is really like to know is whether I need a relay or zone control for the pc702 if I use it.

Using the setpoint demand for dhw priority on the 261 is interesting. I'm going to talk yo the Rep tommorow about this.

SweatyInToronto

The setpoint functionality on the 261 is pretty limited from the manual compared to the 263 for example. No setpoint override for example which is a good safety feature. The 263 has dhw anyway so wouldn't need the setpoint on it.

The 263 looks like a less expensive alternative to the 274, handling 2 stages instead of 4.

Zman

Are your boilers single stage or 2 stage? If they are single, the 2 stage controller will work just fine for 2 boilers.

SweatyInToronto

2 stage yes so pc702 on its own is enuf. The aquastat can provide dhw demand signal is what ur implying?

Zman

I am picturing a 3 pole / double throw relay with a 24 volt coil that would be energized by the aquastat.
The heating circ or controller would be wired to N/O (it opens on DHW call)
The DHW circ would be wired to N/C (it closes on DHW call)
The signal to setpoint demand on the Tekmar would be wired to N/C (it closes on DHW call)

The only weakness I see with the plan is that there is no DHW timeout feature. I usually only worry about that for second homes where a malfunctioning aquastat can cause the house to freeze.

SweatyInToronto

Right, that's a concern here in a multi unit property mainly if there were an extended power outage. After an ice storm power was lost for over a week once!
Not likely but tank water cools substanially.
It might take an hour to reheat. The extra hour wait for room heat is small compared to the week already without. Not a big deal.

Getting a backup generator for the boiler room would be a good idea though and I will add it to the wish list.

Assigning one boiler to dhw only would be another workaround but is there a way to do it without hard piping it? Would not mind alternating which one services dhw annually manually with valves to even wear. Also then if that boiler needed a repair could switch to the other one. Is that feasible?

SweatyInToronto

Spoke w dealer and they referred to applicantions page which is similar idea, although they suggest 2 pole. So it's approved method as well.

Zman

2 Pole would work. You would energize the coil and the tekmar demand terminal both off the aquastat (in parallel)

SweatyInToronto

Great thanks Zman, the dealer maybe wasn't familiar with this approach off hand or wanted to sell new product but glad now and hope to make it happen. Thanks everyone for your ideas as well!

hot_rod

Zman said:

A couple relays would be $50 and would do the same job. If you are worried about the next tech figuring it out, just leave a wiring diagram and label the relay.

If a tech cannot figure out a RIB, which has a wiring diagram on it, they need to be in another business

SweatyInToronto

I'm sure they could but I want to understand it too! Thanks for idea though 👍🏼

SweatyInToronto

> @Zman said:
> 2 Pole would work. You would energize the coil and the tekmar demand terminal both off the aquastat (in parallel)

I guess diff with the HX is there are two pumps to activate, the loop to boiler and the loop from HX to tanks.

Currently in our standalone the pump from boiler to tanks runs continuously, which seems inefficient. It could post purge but after that a waste and maybe cools water off faster no?

Would 3 pole be needed for this?

Zman

Depending on the ratings, you may be able to run both off the same pole

hot_rod

SweatyInToronto said:

> @Zman said:

> 2 Pole would work. You would energize the coil and the tekmar demand terminal both off the aquastat (in parallel)



I guess diff with the HX is there are two pumps to activate, the loop to boiler and the loop from HX to tanks.



Currently in our standalone the pump from boiler to tanks runs continuously, which seems inefficient. It could post purge but after that a waste and maybe cools water off faster no?



Would 3 pole be needed for this?

You are correct, if the pump continues to run and the boiler is not firing, the boiler becomes a cooling tower, of sorts.

Sounds like the entire system could use some remodel and upgrading, maybe control and piping changes.

SweatyInToronto

Indeed. We are planning to add boiler protection at least the manual type. Better than what's there now which is nothing.

Since it's likely we'll upgrade boilers to hi eff in maybe 7 to 10 years my HVAC guy, who is very good in case he's reading, didn't think the investment for automated made sense and I agree as we have a limited budget.

Would u think there are net savings from having a HX if the dhw boiler its replacing is roughly as efficient as the hydronics?

SweatyInToronto

> @Zman said:
> The only weakness I see with the plan is that there is no DHW timeout feature. I usually only worry about that for second homes where a malfunctioning aquastat can cause the house to freeze.

With the 261s setpoint is there a post purge function or can this be set up with the relays? I see a lot of options for handling post purge on the 263 and 274 but nothing mentioned in the 261 info which leads me to believe there isn't any.

If so is that a concern as the dhw would heat exchanger very high. If the return water cooled a lot from the duration of the call or just after wwsd ends in the morning say could it lead to a thermal shock?

The boiler protection planned would just be to manually use in the shoulder seasons mainly and wouldn't raise temp that much initially.

But in any case if dhw loop was 180 and ended suddenly and if the boiler loop cooled down to 90 hit the hot boiler what would happen?

Zman

You could do pre/post purge with relays but they get fairly expensive. I would have to see your proposed piping to see if there was a need. As for thermal shock, you need to keep in mind that boilers usually see 70 degrees or lower at startup.
I would be surprised if you need pre or post purge.

hot_rod

I think an overall assessment might be wise.
Building heat load, type of emitters, piping and pumping, etc

If the boilers are oversized and you have low mass emitters, return protection is less if a concern.

I don’t think the 261 or 702 have DHW function per say. No pump relay or time out function, they are mainly ODR and staging relays.

Timing out the DHW could create problems in a multi family application? That too depends on DHW storage, production, and recovery rate that the boiler and HX are capable of. You don’t want to stop a legitimate DHW call based on an arbitrary time?

All that considered may be why they are separate now?

SweatyInToronto

I guess the diff at startup is that the boiler is cold too. After a dwh call not so much.

Maybe could take a step back and rethink however the dhw boiler had a bad leak and we're worried about its health and lifespan without needing more repairs. So time seems more of the essence.

My intuition is that dwh calls shouldnt last more than 10 to 15 mins. Demand is intermittent thru day and I'm more concerned with short cycling than timing out. The building holds heat well and usually complaint is that its too hot so I suspect there is reserve btu for dhw. Not sure why it is the way it is now but I think it was oil heat when they put in the gas dwh boiler so they probably were moving off oil and didn't want to burn more maybe?

702 has dwh I believe. Not sure how configurable but can check. Manual looked very similar to 261 like a knockoff with dwh but maybe came first. Looks like less $$ but don't have quote yet...

Maybe chance of thermal shock not a biggie. I will try to get a diagram and/or photos.

Thanks!

hot_rod

We are all spitballing here without some data, heat load, number of units for the DHW calc, what size are the current boilers, etc.

What temperature are the 100 gallons tanks maintained at. Mixing valve? DHW recirculation?

Any legionella concerns that may dictate maintaining tanks at 140F or higher?

If the ODR is configured properly and working, I would not eliminate that. From the quick review it doesn't look like the 702 does anymore than the 261?

It looks like maybe the 702 can communicate via side connections communication ports to the Taco relays? That is where then priority and time out function would probably reside, in the relay box not the 702.

SweatyInToronto

Good points Bob. Ill answer these and attach photos,diagtam on Monday or Tuesday.

SweatyInToronto

I've attached some photos of the layout below, and will attempt to answer some of the questions. Also I have a short video but didn't post yet, but can if that helps.

There are two hydrotherm atmospheric hydronic boilers rated 300K input and 240K output each installed 2006, so hopefully have 10 more years in them.

There are 21 bathrooms, and 21 kitchens, 2 washers that are used by the residents. About 45 people live there in the building. There's is 2 laundry sink and 1 utility sink that are rarely used.

There is a single RBI spectrum 199K domestic hot water boiler installed in about 2000 and 2x100 gallon tanks put in 5 years after that. The tanks are currently maintained at 125 degrees and there is no mixing valve. Apparently this temp will kill legionnaires but more slowly than at 140. Also I suspect that the fact the storage circulation pump runs constantly that there is less of a chance for that to occur as water is not stagnant.

The code for new installations is 140 degrees. In the new installation there would be a mixing valve.

With 199K at 125 degrees with 200 gals, no one is complaining.

On average units are 700 square feet and have about 2-3 radiators that are low and long, perhaps 8-15 feet long. I think they are cast iron. Space heat is more than enough on the coldest days.

For DHW, it's now between a Laars Mini Therm 225K or a
500K heat exchanger with a low loss header, for both the same price (except the HX might need extra $ for control to handle post-purge and timeout) and it uses an extra pump which is extra electricity.

The former is simpler, but might end up going to the HX anyway in 10 years when replace hydronics. The latter is more complex but could presumably keep it when we replace hydronics eventually.

The tanks may need to be replaced in any case in 5 years perhaps.
They seem ok though.

Looking at the 702, which we don't have yet, I don't see any special functions for the DHW. It looks pretty much like they have called the 261 setpoint function a DHW priority function. Not sure which one came first but one or the other looks like a knock off! I don't see a timeout function on either. So we would need a 263 or a 274 from Tekmar to handle those functions if they are necessary.

Hope this explains the situation. Know it's a lot already but let me know if I can provide any further information. Thanks for your input again!