Honeywell T775R2035 ?

james patrick

Anyone used one?

Looks like a way to control a buffer tank temp. Based on outdoor reset?

wogpa67

I haven't used the Honeywell.
The Tekmar 256 would do it, and it's cheaper and very reliable.

james patrick

I want the buffer tank to be the boilers only load and its temperature maintained at minimum required.

System will draw heat out of the buffer tank as thermostats require heat.

When the buffer tank temperature drops below where ODR needs it to be some device must issue a "heat call" to boiler TT terminals. Thermostat won't work.

As temperature in buffer tank is variable, it can't use a standard aquastat.

james patrick

A Tekmar 256 needs an "input heat demand"

SWEI

Just jumper those terminals and it will maintain the ODR setpoint temp.

wogpa67

Is the system zoned? If so the zone control would give it the heat demand. If not a RIB could be used to initiate the demand.

I always try new to me controls at my house first. I want to know the up and downsides of them before getting the late night phone calls.

I just read the brochure on it. I will try one out at some point , has a lot of nice features.

james patrick

A boiler demand is required in order for the 256 to provide heat to the heating system. A boiler demand is generated by connecting terminal T(7) to terminal C-(9) through a switching device. Once the switching device closes, the Boiler Demand pointer is displayed in the LCD. The 256 calculates a BOIL TARGET supply temperature based on the outdoor air temperature and settings.

When the 256 determines that boiler operation is required, the Boiler contact terminals (5 and 6) close. While the Boiler contact is closed, the burner segment in the LCD is displayed.

SWEI wouldn't that act the same as jumpering the boiler TT & run the boiler over & over needlessly?

james patrick

RIB ?

wogpa67

It's an enclosed relay.

I am very familiar with all of Tekmar's controls and how they work.

Is this a zoned system? Does it have a zone valve or circulator control?

SWEI

Won't the 256 fire the boiler as needed to maintain the calculated temp at the sensor? If you open the TT terminals, it will let the tank temp drift down until they are closed -- or did I miss something?

Tack SR501-OR-4 might also work, and costs even less.

RIB = Relay In a Box.

james patrick

Zone valves

wogpa67

So your end switch from zone valves would initiate the heat demand to the whatever ODR control you use.

james patrick

What would control buffer tank differential ?
How often would boiler fire ?

wogpa67

Any ODR control you put on it would control the tank temp.
The boiler would only fire when low tank temp minus differential was met.
The 256 which I use on Geo buffer tanks is a good control. User friendly and all the parameters are setup by the installer.

SWEI

This is a very standard ODR control setup -- and yes, your end switches or zone control can make the call. Diagram in the top right portion of this shows the wiring clearly.

james patrick

Thanks, guys

As I want the buffer tank temperature controlled separate from any system "heat call" it looks like a Tekmar 256 with T7 jumperd to C (boiler demand) should work fine.

The sensor wired to terminal T1 to C would be placed in the buffer tank aquastat well instead of on the boiler output. Boiler would fire when buffer tank cooled to 1/2 of the programmed differential below the outdoor reset controlled temp.

james patrick

I hope my post above configuration will work?

The Honeywell T775R2035 would also do it, but costs more.

wogpa67

As Spock would say what is your logic?
Are you wanting to keep this tank at a setpoint all year?

james patrick

Buffer tank needs to be warm to hot about 9-10 months per year, zone 7 Crested Butte Colorado

james patrick

Thinking of using the IFTTT app on Apple IPhone along with WeMo internet controlled switch.

Something like:
If outdoor temp > 65*F for 3 days in a row turn off Tekmar 256 power.

SWEI

The 256 and the SR501-OR-4 both have WWSD. The taco is fixed at 70°F, the 256 is adjustable.

Shoulder seasons are tricky, especially with higher mass buildings and tight reset curves. With DDC, we sometimes average ODT across the past 24-48 hours and then look at the indoor temp to make the call. Lacking that, a manual switch can sometimes prove to be the best answer.

james patrick

Tight reset curve?
DDC?

james patrick

DDC = Direct Digital Controls

SWEI

Tight reset curve means one which, when paired with a reasonably well-balanced balanced system will produce stable indoor temps despite not having a thermostat.