Tekmar 362 Mixing Return Sensor - Used in heat mode?

Al Roethlisberger

Question about the Tekmar 362 Mixing Return Sensor - Used in heat mode?



Per the Tekmar 362 manual:



[quote]



Mixing Return Sensor

Connect the two wires from the Mixing Return Sensor 071 to the

Com and Mix terminals (11 and 12). The Mixing Return Sensor is

used by the 362 to measure the fluid return temperature from the

snow melting slab.



[\quote]



I will be using the 362 in "mode 1" for heat, not snow melt, so based on the description above I assume that the "Mixing Return Sensor" is only used/enabled when in "mode 2" for snow melt functionality.  In other words, for my heat application is it correct to conclude that I will not use this sensor at all and would leave terminals 11 and 12 unused?







This is not to be confused with:



[quote]

10K Sensor

Either an Indoor Sensor, Slab Sensor, or Zone Control can be

connected to the 10K input. If a sensor is used, connect the two

wires from the sensor to the Com and 10K terminals (14 and 15).

[\quote]



or



[quote]

tekmar NetTM Device (tN1 / tN2)

A Room Temperature Unit (RTU) 062 or 063, Remote Display

Module (RDM) 040, or a Remote Start / Stop Module 039 can be

connected to the tekmar NetTM (tN1 / tN2) input. Connect the Com

terminal from the appropriate device to the Com terminal (11) on the

362. Connect the tN1 or tN2 terminal from the appropriate device to

the tN1 / tN2 terminal (13) on the 362.

[\quote]





Although I do have one other question related to these two sensor inputs.  Is there any advantage to using the "10k" versus NetTM connection for an internal temp sensor?  If not, I wonder why Tekmar offers both options?



And I assume that in that application one would use one *or* the other, not both at the same time(that is, two interior temp sensors one each on the 10k and NetTM connections)?





Thanks,

Al

Al Roethlisberger

Related - thermostat, 10k, and Tekmar Net sensors, not at same time it seems?

Related to the 2nd question above, as I've read through the data brochure for the 362 further, it starts to sound like the use of a thermostat(connected to "mix demand"), the use of a 10k sensor, or the use of a Tekmar Net sensor like an RTU are mutually exclusive.



Originally I interpreted the instructions to indicate that one would use the traditional thermostat to generate the "mix demand", then the 10k or RTU was used by the 362 to fine tune.  But now I'm reading the instructions to sound like when one chooses to use a 10k or RTU, one simply keeps constant voltage across the "mix demand" connector(where one normally would connect a thermostat), and the 362 uses the data from the 10k or RTU to trip "demand".



Here's the text from the 362 data sheet:



[quote]



Section B2: Alternate Mixing Demands (Mode —1—)

In addition to using conventional thermostats to provide a mixing demand as described in Section B1, the 362 can use a number of other

methods to provide a mixing demand.



10K INDOOR SENSOR (10K = INDR)

Set the 10K item to INDR to add an indoor sensor for temperature control of a single zone

mixing system. The indoor sensor is connected to the Com and 10K terminals (14 and 15).

In addition, power must be applied to the Mix Demand terminals (1 and 2) as described in

section B1. With the indoor sensor connected, the 362 is able to sense the actual room

temperature. With this information, the 362 provides a more constant water flow through the

mixing system. At the same time, indoor temperature feedback fine tunes the supply water

temperature in the mixing system to prevent over heating or under heating. To adjust the room

temperature for the mixing zone, use the ROOM Occupied or UnOccupied setting in the Adjust

menu at the control.



ROOM TEMPERATURE UNIT (RTU) 062, 063

If the mixing system consists of a single zone, temperature control of that zone can be provided

by using an RTU. The RTU is connected to the Com and tekmar NetTM tN1/tN2 terminals

(11 and 13). In addition, power must be applied to the Mix Demand terminals (1 and 2) as

described in Section B1. With the RTU connected, the 362 measures the actual room

temperature. With this information, the 362 provides a constant water flow through the mixing

system. At the same time, indoor temperature feedback fine tunes the supply water

temperature in the mixing system to prevent over heating or under heating. The RTU allows

the user to adjust the desired room temperature at the RTU. Remote sensor capability is also

available through an RTU as described in the RTU data brochure.



[\quote]





So, *if* I have interpreted this correctly, if I chose to use an RTU, I would simply provide constant power to the "mix demand" and not use a traditional thermostat, and the RTU would in combination with the 362 trigger a "mix demand"??



Al

Al Roethlisberger

Did some more reading, but still not 100% clear.

OK, I went home and re-read my 362 manuals that came with the unit and I think it partially answers some of my questions.



It seems clear in their design guide 362-2(which is similar to my installation) that when one uses a sensor like the RTU, a traditional thermostat is no longer needed.  The diagram shows 120V/AC applied directly to the "Mix Demand" constantly(although also shown in the diagram with an optional relay).



This still raises some questions though.  In the 362 manual, it says that when "mix demand" is closed/called, power to the pump relay is activated to run the system pump(and boiler loop pump).  So I'm wondering if one keeps power to the "mix demand" connection 100% of the time if the pump(s) will run continuously, or if the 362 will use the signals from the RTU and computed parameters to only run the pump(s) as needed?  This isn't clear in the manual.





Al

Mark Eatherton

They run....

If their circuit is calling, they run, until WWSD kicks in.



ME

Randy Baerg

362 mixing return sensor only in Mode 2

The Mixing Return sensor on a tekmar 362 is only used in Mode 2 for a snowmelting application. In this application it allows the control to provide a maximum Delta T between the Mix supply and the Mix return temperature to help reduce thermal stress on the snowmelt slab.

In Mode 1 for building heating a mix return sensor is not used.

NRT_Rob

you can use it three ways

1. put on a thermostat and use it as an outdoor reset only control, but in that case you should probably use a different controller.



2. put on the indoor sensor, run it constant circ. this means you change room temp at the controller.



3. put on an RTU, run it constant circ, but you control room temp at the RTU instead of the controller.



these days if you do constant circ there are plenty of good options for reducing pump energy, either ECM pumps or variable speed (see other thread on the main wall debating this left and right).

Al Roethlisberger

Yes, I plan to go the RTU route.

Although I don't plan constant circ, just kick in the primary and secondary loop circulators when there is a call for heat.





But the question still remains....



From the 362 manual:



[quote]

ROOM TEMPERATURE UNIT (RTU) 062, 063



If the mixing system consists of a single zone, temperature control of that zone can be provided



by using an RTU. The RTU is connected to the Com and tekmar NetTM tN1/tN2 terminals



(11 and 13). In addition, power must be applied to the Mix Demand terminals (1 and 2) as



described in Section B1. With the RTU connected, the 362 measures the actual room



temperature. With this information, the 362 provides a constant water flow through the mixing



system. At the same time, indoor temperature feedback fine tunes the supply water



temperature in the mixing system to prevent over heating or under heating. The RTU allows



the user to adjust the desired room temperature at the RTU. Remote sensor capability is also



available through an RTU as described in the RTU data brochure.







[\quote]











So, *if* I have interpreted this correctly, if I chose to use an RTU, would I have to still provide constant power to the "mix demand"(terminals 1 & 2) to actually trigger a "mix demand" when the RTU calls for heat?



It isn't very clear.





Thanks,



Al

chris_69

Why designed that way?

Maybe someone from Tekmar (or otherwise knowledgeable) is reading this.



It seems that if the RTU or room temperature sensor is saying that the room temperature is at or above the desired point, then there is no reason to run the system circulator, and that power to the circulator should be removed.



Why doesn't it do that?