Solar Setback--Tekmar or other?

Ron Schroeder

Hi gf,

Are you actually getting over heating or do you just want to keep the boiler temp as low as possable. If the solar gain is heating the house up enough that the thermostats don't call for heat at all, lowering the boiler temperature will not prevent over heating.

How many zones do you have? If you have more than one, is one zone overheating while another one isn't? (like the east zone in the morning and the west zone in the afternoon?)

Ron

gasfolk

Dual outdoor setback?

Is there an outdoor reset control, perhaps using dual (north and south side) outdoor temp sensors, that will adjust supply temps for daytime solar gains?

Our 1920's house gets a substantial daytime solar benefit, and we believe lower daytime supply temps would reduce daytime cycling and better match daytime heat loss. We have a Tekmar 352 control.

Thanks,

gf

hydronicsmike

North and South

I dont know if anyone has attempted this with an Outdoor Sensor on the North and the South side of a building.

tekmar can typically compensate the supply water temperature based on Indoor Temperature Feedback that keeps Solar and other heat gains in mind. Sensors or RTUs are typically used for this. The Supply Water temperature is lowered as the solar or additional heat gain hits the space. If you have an 054 RTU connected to your 352, it should be able to take care of this.

Please call, should you have further questions. 250-545-7749.

Regards,

Mike

Bob Eh?_2

You could potentially do this several ways..... Use TRVs, a separate thermostat, or probably some system controls based on Tekmar TN4 in the effected areas. It would depend on your current emitter layout as to what can be done and at what cost.....

I sent you an Email offline... Did you get it?

Bob

Unknown

just to reaffirm, we use indoor feedback to deal with that issue all the time. In the vast majority of cases, it is more than adequate to the task.

Mike T., Swampeast MO

Will be experimenting with that exact thing this heating season on a Vitodens.

Vitodens controller doesn't allow two outdoor sensor for temp diversity setpoint modification, but you can fool it...

Connect two outdoor sensors through a double-pole, double-throw relay with the common contacts going to the reset control. Was told to use relay with gold plated contacts (common in good audio equipment) to keep contact resistance to an absolute minimum. Viessmann told me that the momentary connection loss and/or erroneous reading when the switch occurs won't cause a problem as it won't be long enough in duration for the control to detect a fault. Check with Tekmar to make sure the switching won't be a problem.

Will first control the switchover with a simple timer. Will start with four hours centered around solar noon. (In my latitude that's the time that solar gain peaks.) If things work out will try to devise a switching scheme based on solar intensity.

gasfolk

Sensor Locations?

We are planning a boiler upgrade and are trying to choose locations for sensors for a data-logger, hoping to capture the maximum meaningful data (on how our current system works) over the next heating season. We hope design supply temps will be below 125*, so maybe we should set our high limit to 110* or 120* during data acquisition.

We know passive solar heating is a major factor for us, but we don't yet fully understand how it is affecting our system performance and sizing issues. On at least some days, we have seen solar-induced overheating by 5*, and we understand the benefit if the boiler shuts down, but is that all we need to consider? Are there parameters we can and should measure to get a better understanding of this?

We have a one-zone, two-pipe, converted-gravity system (small areas of RFH are separately controlled, but these are small) that heats comfortably and uniformly--a testament to the Dead Men--but the current boiler is 350 MBH and depending on the data-logger, the replacement may be much less than 120 MBH.

(We have benefited from many good comments on and criticisms of our sizing issue. See http://forums.invision.net/Thread.cfm?CFApp=2&Thread_ID=27817&mc=39 )

Thanks for any advice or comments you can offer us,

gf

gasfolk

Thanks,

I will look for it asap.

gf

Ron Schroeder

Hi gf,

I think you are contemplating a geothermal HP/gas boiler hybrid system. Do you have A/C now? How many tons of A/C do you need? For gas, will you be using natural gas or propane? Have you compared btu/$ for the heat pump vs. btu/$ for gas? Where are you located? When you have over heating, is it in rooms away from the thermostat or in the room with the thermostat too?

If you are sizing a heat pump with suplimental fuel, it is usually best to size the heat pump for the cooling load.

gasfolk

Good questions...

We will install central A/C but note that, depending on our heat loss, the differential cost for a GSHP could be repaid in a reasonable time (for us, since I'm never again moving).

Sizing is the critical question. We understand the potential for unitary or hybrid systems, but our heat-loss estimates vary from 44 to 120 MBH (see the above referenced thread for details). Modulation makes boiler load matching fairly easy--any built-in, Manual-J over-sizing will be modulated away. But GSHP installation varies roughly linearly with price, so inflation in the heat loss can make this option economically unviable. If, for example, we could be sure that our true heat loss is 50 MBH, then we could go with two 3-ton GSHP units and be done with it.

A necessary assumption is the reliability of local climate/BIN data, and from our experience, the sun will continue to rise and to set. We explored with many others (in the above referenced thread) other possible sources of discrepancies, particularly passive solar heating.

For these reasons, our focus has shifted to data acquisition--installing sensors for data-logging so we can improve the modeling/heat loss estimate of our house. From your questions, we realize that we should wire the system *now* to collect data for both heating and cooling, in case we choose the hybrid model you mention. Any suggestions to make sure we capture all the parameters of solar influence on our heat loss?

Thanks for your ideas,

gf

gasfolk

South side sensor alone?

If your south side to north side sensor differential peaks at 15* around noon, with a smooth slope before and after, and with no differential at night, would there be a drawback to just directly wiring the south side as your outdoor sensor?