I'm thinking about smartening up our radiant system a bit, and was curious what the thinking is about the benefit of using outdoor reset on a 3 way mix valve that feeds our radiant zones versus using outdoor reset on the indirect water heater that supplies the whole system? We have geo for forced air/AC and hot water (synergy 3). Synergy 3 supplies hot water to an ergomax e44 indirect water heater. The aquastat on the ergomax controls the geo pump, so we run about 110 in the winter. There is no ODR on it, just a single set point with about a 5 degree diff. Last summer I backed off the ergomax temp to about 95 for preheat of DHW. We replumbed the radiant/hot water system last year to add the ergomax as well as add more zone control of the system. It's working very well, and supplies our entire heat load for the house without the forced air kicking on. We have the viega basic heating control, which was left over from the original configuration. It is running the mixing valve, without ODR, but as I understand it is capable of this. Should we configure the mix valve to do ODR, or would we benefit more from adding ODR on the ergomax so the boiler water is the right temp given heating load? Or should mix and boiler ODR be combined? It seems like having ODR on the mix temp may offer a bit of comfort benefit via not overheating when temps are moderate outside, but boiler reset might offer the same benefit and save costs. The house is warmboard on 2 levels with slab tubing in the basement, which almost never needs to run as the basement temperature seems to hover around a comfortable 68 regardless of weather.

reset on the mixing valve will not help your geo efficiency.

reset on the tank will.

reset the tank. This will give all the potential benefits of reset instead of just the comfort benefits. No need for mixing valve after that. If you need 110 at design, most of the time you could probably run about 90 degree.

Thanks.
It seems the viega basic heat control (http://www.viega.net/cps/rde/xbcr/en-us/Viega_ProRadiant_Basic_Heating_Control.pdf) is designed to operate the mixing valve, but given that it has a temp sensor, dry contact switch to control a boiler and outdoor reset abilities, would it be able to switch on the boiler (geo) to make hot water? Or do I need a boiler reset product?

If I need a boiler reset product, should I be looking at tekmar? What is the most cost effective tool to do this?

Thanks

I would not use anything unless it had the ability to provide a predictable firing differential for the boiler. I don't think that's a case with a mixing controller.

Tekmar 256/260 would probably be the cheapest upfront. we generally use TekmarNet4 systems, or Net 2 systems, as they add indoor feedback (requires tekmar thermostats that are tn4 or tn2 compatible) which means the system can respond quicker but more importantly can run at even lower temperatures oftentimes... say, whenever heat gains from other sources are contributing to your loads.

is that more cost effective? depends on the size of the load you are servicing, I suppose. If you call it a $1000 up front differential, you'd have to figure out the difference between that and just plain reset. I'm not sure how fast that would really cover costs but on most larger geo systems I think it's a generally good investment.

Thanks, very helpful advice.
For now, the tekmar 256 looks like a good option.
A couple of additional questions-
First, the 256 requires a "boiler demand signal". What would I normally connect to this? And does that mean it won't maintain temperatures in the ergomax unless there is a call for heat? I'd like to keep the tank at least 85 or 90 degrees for DHW preheat.
Second, it looks like my house would be a "low mass radiant" system in the 256 configuration. Are those boiler temperatures appropriate for the GSHP? It appears the design temp would be 140, and I'd probably want to use the boiler max temp for the heat pump, say 115 or so to keep the geo system running efficiently. Or would I want a lower design temp for GS heat pump boiler.

Jim

demand signal is just your thermostatic demands... zone relay TT out, etc.

it will not maintain temp without a demand. if you want to put an aquastat on the tank for a minimum temp maintainence you can do that, or you can jump out the heat demand on the controller for a permanent demand situation.

You would use a reset curve set up for your system requirements. If 110 degrees heated your house ok, your design water temp would be 110 degrees. Or lower. You want the lowest you can make work to maximize your geothermal efficiency. However, you mention a 5 degree differential on the tank, I doubt that is adequate for buffer run time surety. Probably want a bigger number on that.

Thank you.

If I used the tekmar 400 as an option to get reset, would it also provide the ability to add zones to a remote manifold? It seems to support that. And it seems the 400 won't support a minimum temperature in the range I need on the indirect water heater - it will maintain 140 degrees as boiler protection, but this is about 50 degrees higher than I need. Would I also have to wire the aquastat to keep the minimum temperature? Thanks

I have not used the 400. Normally we'd use a 420 and appropriate zone controls/thermostats for that controller, but for a minimum temp situation you'd probably want an aquastat for that or some real inventive setups.