Distribution Losses

[DaBackBurner]

Thanks to this forum my inquisitive mind has started to work again. Thank you.
My workshop has infloor and controlled by outdoor reset and after a year and half have found it to be a great system. Now I would like to put the house emitters on outdoor reset as well, fin-tube and wall panels, to not only gain the benefit of possible longer storage times but also gain the benefit of returning with lower water temperatures to help in the stratification area. I've been kicking around ideas such as injection mixing, variable speed delta T and motorized valve mixing. My Garn is plumbed as a secondary into my primary house loop with a Flat Plate in the house.
My question is which will provide me the lowest distribution loss in my underground lines? The answer seems to be mixing prior to going into the underground but maybe I'm just reaching.
If I do mix or inject or so forth, how can I 'bypass' the mixing aspect when I'm heating DHW? I've searched long and hard and while on/off injection or variable speed injection with DHW priority will work, I will still flow the hottest temp from storage this way and it seems my underground will experience higher heat loss with hotter water flowing in it.
A mixing valve with a controller seems to fit the bill, but how do I send a signal to it to bypass outdoor reset (open the valve all the way) when DHW calls for heat? Or, should I just consider a bypass loop with a diverter valve that would bypass the mixing valve when there is a call for DHW?

 

[TCaldwell]

I am not sure my way is what you are looking for but i installed a taco 3 way setpoint i valve right off the back of the garn before my flatplate in my garn barn. this way the designed lower water temp is flowing in the pex underground and the hotter water quickly returns to the garn. The i valve is motorized and comes with a supply sensor with a temp dial on top. I easily heat my dwh with 130deg supply from the i valve. during colder weather I dial up a desired supply temp. not as sophiscated as outdoor reset but it works well. The valve is 1 inch. a 15-58 on low easily produces 200kbtu with a large delta t.

 

[bpirger]

I agree with that notion, keep the hottest water inside the Garn. So ideally then the HX would live just outside the Garn, and you could use a variable speed controller to pump the water out of the Garn through the HX. The pump running on the house side of the HX would just run at a fixed speed...pushing a constant temp water.

Depending on how much you lose in your piping, you'll get a predictable decrease in loss.

Tekmar controllers have the outdoor reset function, though I don't know if you can "set" the temperatures it ranges....though you could likely adjust the curve to what you want I'd guess. As for the DHW setting for the target, I don't think there is an explicit setting for boiler target for DHW vs. boiler target for heating. I have wished for this same exact thing.

These are the kinds of things that make me want to put together a little microcontroller and a whole bunch of relays, variable speed drives, and temperature sensors. Then everything can be controlled, depending on all the relevant temperatures, etc.

Though at the end of the day, I'm not sure one would gain a whole lot more in efficiency.....but it sure is fun!

 

[DaBackBurner]

Thank you for the responses gentleman...alas my heat exchanger is in the house, maybe I will change that this summer or make my own microcontroller, as you say...it would be fun...or somehow send a phantom signal to the outdoor reset controller during DHW that says it's -20deg during that cycle. He, he lots of fun. I think my bypass loop would work as well but that requires the torch again, and I gotta believe with all the wiz-bang stuff out nowadays it should be able to be controlled in a way that I want. I wonder if a dif controller is all that I need, that would sense a burn, supply full open signal to the reset controller, heat dhw to say 170, then return control to the reset controller. I could preheat the well water using the supplying reset temperature in a similar manner to nofossils DHW. All kinds of fun things to explore I guess.

 

[TCaldwell]

I was all set to buy the tekmar valve, actuator and controller, although a probably a better way to go but at twice the price as the taco. the other way would require the hx in the garn barn but a small static speed pump off the back of the garn to the hx, then on the pressureized side a taco setpoint circ with outdoor reset built in. the hx acts as a injection loop.

 

[DaBackBurner]

Yep exactly, it seems more off the shelf controls could be used to do what I want if my heat exhanger was in the Garn Barn. Guess I'll be getting the torches and wrenches out again this spring, I really don't mind actually, there are a few other adjustments I could do, while the tools are out.

 

[heaterman]

Tom's solution of a fixed setpoint type controller is very simple and reducing the water temp going through your underground will definitely drop the heat loss there. I use a lot of the particular device he mentioned and they work very well.

I find that unless you have a serious DHW load or a tank that is marginally sized, 130-140* water will do a decent job in most indirects. Those things transfer heat like crazy. I fired up an oil boiler today that was a no heat service call. House was at 63* and the DHW tank was about 70* water temp. When I flipped the switch on the boiler it showed a water temp of 70*. Within 25 minutes the 45 gallon indirect was at 125* which was virtually the same as the boiler temp at that point. Basically, both gained temp at the same rate and this was with all 3 zones in the house calling for heat also. Pretty much proves you don't need 180* water to recover an indirect. The boiler in this situation was a 105,000 btu Viessmann Vitorond 100 so it's not like there was a ton of horsepower driving everything.

I think that I'd try reducing the water temp out in your Garn Barn before I took hacksaw and torches to your piping and moving the heat exchanger.

 

[DaBackBurner]

Hmmm...interesting stuff. So my underground would be at a setpoint presumably set for design temps or possible a bit higher for DHW almost like partial outdoor reset. And I could adjust this. If I needed to I could always mix down after that in the house for full outdoor reset, although this would probably be an expense not worth the return, unless I put slab radiant somewhere, which I can't envision, but I could non-the-less. I would still need to haul out the hack saw and torches to install the valve but I have to regardless. It would require less work than moving the heat exchanger and my present expansion tank wouldn't have to be resized or even calculated to see if I did need to resize it. Hmmm...great stuff. Thank you all again. Now I'll be chewing on that, cool. I need to put in a setpoint valve for the other house supply anyway since it is set up as an air coil (blah). The folks couldn't be convinced to go hydronic, and with pybyr's posts and yours (thank you), it does, I have to admit, work very well. I do need to get a different indirect or at least change my heat-exhanger in it as me thinks it is scaled up from my well water. Thankfully my children are not teenagers quite yet. Thanks again.

 

[bpirger]

I find my DHW essentially needs boiler supply to about 5 degrees warmer then the target....though it will take some time. BUT, I'm not sure unless you take more than 2 showers in a row, long showers, you'd ever run out of hot water. I set my DHW at 115 these days, plenty hot, and it will heat until 118 and then shut down. 50 gallon tank.

I like the idea of limiting the boiler supply to say 140....no need to be cranking in that 170 water for radiant. I'll have to look into my Tekmar 363, I bet I can set the max limit on the boiler supply manual, and just let it top out at 140. I wonder if I'd get a longer time out of my GArn 1500 firing. I know my supply temp out the back drops like a rock after firing stops within a couple of hours....all that loss driven by much higher temps than I need! Might make the pumps cycle more often....but that presumably doesnt matter. Most certainly worth a try.

Could one have two pumps in the loop behind the garn going to the HX....using one for DHW call for heat and mixing to a higher T and one for radiant call, mixing to a lower temp? This would require pumping water through a stationary pump....but in this application, it would probably be OK. Not the cheapest way though....

 

[pwschiller]

I am not sure my way is what you are looking for but i installed a taco 3 way setpoint i valve right off the back of the garn before my flatplate in my garn barn. this way the designed lower water temp is flowing in the pex underground and the hotter water quickly returns to the garn. The i valve is motorized and comes with a supply sensor with a temp dial on top. I easily heat my dwh with 130deg supply from the i valve. during colder weather I dial up a desired supply temp. not as sophiscated as outdoor reset but it works well. The valve is 1 inch. a 15-58 on low easily produces 200kbtu with a large delta t.

The Taco iSeries Setpoint valves also have a 15 degree setback feature that would make it fairly easy to have two different mix down temps for different purposes. For example, you could put the setpoint at 145 F, which might work well for quick DHW recovery, but trigger the setback function when DHW isn't calling for heat, so that you're mixing down to 130 F for just radiant zones.

Or, if someone had a mixture of radiant and baseboard zones you could take advantage of the setback feature. Put the setpoint at whatever you consider to be the minimum for the baseboard zones (e.g. 160 F), but trigger the setback feature when baseboard zones aren't calling for heat, so that everything else gets 145 F.

I don't think that the outdoor reset version of the iSeries valve has the setback feature.

 

[bpirger]

Not that this helps others, but the Tekmar 363 DOES indeed provide two different boiler targets, one for heat demand, one for DHW......

 

[DaBackBurner]

Thanks for the additional info guys. I've been reading about this stuff all night and will continue to as it's too bloody cold out tonight to do anything else...besides I enjoy it.