Tekmar 654 Snow Melt IDLE - pumps running full-time

PeterKing

Hello all.

I've got a radiant snowmelt system with a Tekmar 654 control. We want to use the IDLE feature to keep the slab close to the melting point even when there is no snow. The problem is that the circulation pumps run constantly even when the slab temperature is much higher than the target slab temperature.

The app mode is MIX. The control correctly sets the mix down to 0% when the slab temperature is reached. But the SYS PUMP RELAY keeps the pumps running. In a current situation, the IDLE temp is set to 25 degrees. The calculated SLAB TARGET is 25 degrees. Outdoor temperature is 40 degrees. And the slab is reading 54 degrees. MIX is 0%. But the circulation pumps continue to run.

In this scenario, where the slab temperature is fully satisfied and then some, I want the pumps to go off. The pumps are in a boiler room on the first living floor of the house. To reduce heat and noise from this room, we want to limit the running times of the pump without turning off the snow melt IDLE function.

Any suggestions greaty appreciated.

PeterKing

GGross

I believe the system pump is set to run whenever you are below WWSD temperature, whether the slab is up to temp or not. Assuming the system is piped correctly, and wired correctly, this should not fire the equipment any more than is necessary to keep the slab at temperature. The pump running, and not calling for heat, with a mixing valve or pump installed, should not increase the heat in the boiler room

The IDLE feature is generally used where snow melting is of critical importance, or the cost to operate is not being considered.

Depending on how the system is wired you could achieve your goals by taking a call for heat from the 654 control, and wiring it to a separate pump relay, not using the auxillary syspump option on the Tekmar. Then the pump would run only when there is a call to heat the slab, and you could use a relay with built in pump exercising to keep the pump occasionally circulating

In general keeping the pump flowing when you are below warm weather shutdown is a desirable feature as the glycol water mix seems to turn a bit "slushy" when it gets cold and stops moving for extended periods of time.. For my money I would run the pump continuously when the system is below WWSD, and rather than idle the slab at 25 would just run the system on AUTO and let it melt on its own. If this is about saving money, even a little bit, then the only correct answer is to turn off IDLE, IDLE is inherently wasteful and is like that by design, but either way if that control is running the system it will run that pump below WWSD to keep a good flow in the system.

PeterKing

Thanks. It's not about money, it's just that the pumps are large and creates a lot of heat and vibration when running. We are in a flood zone where all mechanical equipment must be above the base flood elevation so don't have the luxury of putting the pumps in a basement away from living spaces.

I'm going to try, as you suggest, to trigger the pump using the call for heat rather than the SYSPUMP output from the 654. Thanks for the suggestion; I appreciate the help.

Doug_7

Hi Peter - We have operated a driveway snow-melting system in Alberta Canada for 24 years using a Tekmar 622 control. We have tried the IDLE function and do not like it for the two main reasons that the pumps run continuously and the driveway slab must be continuously heated wasting energy.

We run the driveway snow-melting system on full automatic control governed by the snow/ice sensor, so that if it is not snowing, the whole system shuts down rather than idling.

The system can go several days at a time without running the heating system and the slab cools down well below freezing, and when it snows again it may take several hours to clear the snow from the driveway, but this has never been a problem for cars coming and going. We prefer to save the money on electricity and natural gas - which could add up to be several thousand dollars per year.

The IDLE function sounds good but is very expensive to operate. I would only use IDLE for a driveway for emergency vehicles.

Our driveway is a ramp that slopes down about 8 feet to enter an underground parkade.

Doug

twinax

Hello All, I have a similar question, I have a Tekmar 664 controller . It snowed yesterday and all the snow melted , course it is cold at night outside but I would think the tekmar should tell the unit to stop heating the slab

Doug_7

The Tekmar 664 controller will tell the unit to stop heating the slab once the snow-ice sensor has gone dry and it has completed a melting cycle. If it is continuing to heat the slab, check if the snow-ice sensor has gone dry.