Lower heating temperatures

[chuck172]

I'm curious if anyone is using 4-way mixing valves, radiant heat, delta t circs., panel radiators etc. to utilize the lower storage water temperatures.
Most heating systems are designed to use 180*. Although pressurized storage hits and surpasses that, it's very limited.

 

[sdrobertson]

I'm using this (broken link removed to http://www.patriot-supply.com/products/showitem.cfm/144293) to keep my temp at 110 degrees when the water returns to my tanks. I have the sensor on the return side of my heat exchanger in my furnace. This way I get a constant return temp so I keep excellent stratification in my tanks. Works really well

 

[chuck172]

I'm not familiar with that type of pump, how does it work. By delta T or does it just keep re-circulating return water until it reaches a set temp?

 

[barnartist]

I also would like to learn more.

 

[sdrobertson]

I found it last year by calling around and I was looking for the same thing but made by Taco. It has a sensor that comes with it and it has a set point for what you want the water temp to be. I set mine at 110 so the circulator speeds up and slows down to maintain this temp. The sensor is on my return off my air handler so when the furnace is not running, the pump is satisfied with the water temp at the probe. When my furnace kicks on, the circulator moves just enough water to maintain the 110. I chose 110 because it heats my house at this time of year. I'll move it up to 130 or so when it gets really cold out. I was having a problem that my circulator was always running even if my house furnace was off and that would total screw up my stratification as sometimes I would return 180 water to the bottom. I was going to use a 3-way valve and just circulate the water in a loop till it got colder but this was just easier as all I had to do was replace my 007 and run a light gauge line into the house. My tanks now stay at 190ish at the top and 110 at the bottom and that temp slowly moves up as I use BTU's out of the tank.

 

[chuck172]

I'm bringing up this old thread because I still don't really know the answer.
Would lowering my supply temperatures from storage to the fintube emitters improve my overall efficiency?
After doing an exhaustive heat loss calculation, I put in enough fintube to lower my water temperature. I can go down to 150*. Now if I bring my 500 gallons of storage up to 190*, put in some type of mixing or tempering valve and circulate 150* water, would it be worth it?

 

[jebatty]

I use a 3-way mixing valve to mix-down hot water from storage at up to 192F to 100F supply to my radiant floor. Floor is set at 61F with 1F differential. Couldn't work better.

 

[ewdudley]

Would lowering my supply temperatures from storage to the fintube emitters improve my overall efficiency?
After doing an exhaustive heat loss calculation, I put in enough fintube to lower my water temperature. I can go down to 150*. Now if I bring my 500 gallons of storage up to 190*, put in some type of mixing or tempering valve and circulate 150* water, would it be worth it?

No it would not improve your efficiency. Mixing down to lower temperatures is done for radiant floors because there is no other choice, and it has nothing to do with efficiency per se, or your question. When there is a choice, as with radiant panels, or, in your case, with over-sized fintubes, the benefit of choosing lower temperatures as regards promoting efficiency exists primarily when lower return temperatures can be used to take advantage of a condensing-type boiler, which you don't have.

But what the extra fintube can do for you is to let you take better advantage of your storage by taking it down to lower temperatures between burn cycles. So instead of a mixing valve you might want to look into a diverting valve that would recirculate your return water whenever it is above a certain temperature. That way you pump the minimum amount of water, and you can take full advantage of your hottest water.

Have a look at how the Tarm reference designs do it with a diverter valve, which is one way, or have a look at the primary-secondary sticky for the primary-secondary approach, as well as the hydraulic separator method, which is discussed in the same sticky.

Also the ECM variable-speed constant-pressure or constant-return-temperature pumps mentioned above could do the trick if your baseboard doesn't need recirculation to achieve even heat distribution.

--ewd

 

[Jeff S]

I'm currently using a Tekmar mixing control with outdoor reset to control water temp.In my case with my CI Rads I use supply water temps between 100 - 125* F.
When it was -12*F last year my house was a cozy 72*F with 125*F water.

 

[chuck172]

How does the Tekmar 712 mixing valve, (http://tekmarcontrols.com/accessories/712.html) differ from the diverter valve that Tarm sells? Don't both of them re-circulate return water back into the supply to lower emitter water temperatures? How about the delta t pumps? Wouldn't just slowing down the pump speed through the system do the same thing?
Jeff, do you feel that your 660 gallons of storage lasts longer with usable temps of 100-125* than it would at 160-190*?

 

[Dune]

Would lowering my supply temperatures from storage to the fintube emitters improve my overall efficiency?
After doing an exhaustive heat loss calculation, I put in enough fintube to lower my water temperature. I can go down to 150*. Now if I bring my 500 gallons of storage up to 190*, put in some type of mixing or tempering valve and circulate 150* water, would it be worth it?

No it would not improve your efficiency. Mixing down to lower temperatures is done for radiant floors because there is no other choice, and it has nothing to do with efficiency per se, or your question. When there is a choice, as with radiant panels, or, in your case, with over-sized fintubes, the benefit of choosing lower temperatures as regards promoting efficiency exists primarily when lower return temperatures can be used to take advantage of a condensing-type boiler, which you don't have.

But what the extra fintube can do for you is to let you take better advantage of your storage by taking it down to lower temperatures between burn cycles. So instead of a mixing valve you might want to look into a diverting valve that would recirculate your return water whenever it is above a certain temperature. That way you pump the minimum amount of water, and you can take full advantage of your hottest water.

Have a look at how the Tarm reference designs do it with a diverter valve, which is one way, or have a look at the primary-secondary sticky for the primary-secondary approach, as well as the hydraulic separator method, which is discussed in the same sticky.

Also the ECM variable-speed constant-pressure or constant-return-temperature pumps mentioned above could do the trick if your baseboard doesn't need recirculation to achieve even heat distribution.

--ewd

I get confused easily.
I agree that a lower temp to the emitters will esentialy add storage capcity.
I also think though, that running the emitters at a lower temp will add efficiency. Is this not the main reason that in floor radiant tubing is more efficient?

 

[chuck172]

I get confused easily too. Take a room requiring lets say 70*. It's 32* outside. This room has a heat loss of lets say 2,000 btu/hr.
The thermostat opens the zone valve that turns on the circulator. One scenario is 140* water is pumped for a certain amount of time to satisfy the thermostat and heat loss.
The other scenario is 180* water is pumped for a much shorter time to satisfy the same conditions.
I don't know if one case is more efficient than the other. It is for certain that the system pumping low temp heat will allow a given amount of storage a longer period of time before recharging. In other words, lower system temps allow lower use of storage temps.
Now if the emitters are sufficient to allow lower operating temperatures, what is the most economical way of lowering the storage temperature from say 190* to 150*?
I know this can be done with lots of money, but many of us are in this to save money.

 

[ewdudley]

I agree that a lower temp to the emitters will esentialy add storage capcity.
I also think though, that running the emitters at a lower temp will add efficiency. Is this not the main reason that in floor radiant tubing is more efficient?

I'm saying that when we burn something there is a theoretical maximum amount of heat given off as a result, depending on the fuel source, oxygen concentration, and so forth. The percentage of the theoretical maximum that is delivered to the conditioned space is the efficiency.

If lower emitter temperatures can improve the percentage of the heat that goes into the house as opposed to somewhere else, then it can improve efficiency.

Low temperature emitters make it possible to get system return temperatures low enough to take advantage of flue-gas-condensing boilers. In this case efficiency is increased because less heat goes out the flue and therefore more is available to deliver to the house. However, although I suppose there's such a thing as a flue-gas-condensing wood boiler, it's not the type of boiler we're talking about here.

So low emitter temperatures don't allow us to operate wood boilers more efficiency, except perhaps to the small extent that running with lower boiler supply temperatures could improve boiler heat extraction a little, but return temperature and flue gas temperatures must be maintained above certain minimums in any case.

And another advantage lower emitter temperatures would be that the average temperature of storage would be lower, so there's that, but still not a factor that will noticeably affect the size of your woodpile next spring.

Low-temperature emitters are definitely the way to go if you can pull it off; better utilization of storage, more comfort, more even heat, less pumping energy, bragging rights, you name it. But as far a sending significantly less heat up the flue goes, you need a flue-gas-condensing boiler for that.

 

[Dune]

I agree that a lower temp to the emitters will esentialy add storage capcity.
I also think though, that running the emitters at a lower temp will add efficiency. Is this not the main reason that in floor radiant tubing is more efficient?

I'm saying that when we burn something there is a theoretical maximum amount of heat given off as a result, depending on the fuel source, oxygen concentration, and so forth. The percentage of the theoretical maximum that is delivered to the conditioned space is the efficiency.

If lower emitter temperatures can improve the percentage of the heat that goes into the house as opposed to somewhere else, then it can improve efficiency.

Low temperature emitters make it possible to get system return temperatures low enough to take advantage of flue-gas-condensing boilers. In this case efficiency is increased because less heat goes out the flue and therefore more is available to deliver to the house. However, although I suppose there's such a thing as a flue-gas-condensing wood boiler, it's not the type of boiler we're talking about here.

So low emitter temperatures don't allow us to operate wood boilers more efficiency, except perhaps to the small extent that running with lower boiler supply temperatures could improve boiler heat extraction a little, but return temperature and flue gas temperatures must be maintained above certain minimums in any case.

And another advantage lower emitter temperatures would be that the average temperature of storage would be lower, so there's that, but still not a factor that will noticeably affect the size of your woodpile next spring.

Low-temperature emitters are definitely the way to go if you can pull it off; better utilization of storage, more comfort, more even heat, less pumping energy, bragging rights, you name it. But as far a sending significantly less heat up the flue goes, you need a flue-gas-condensing boiler for that.

I have installed a great many radiant floors. I started installing them before the MOD-CON boilers were available.
I was always told that the lower opperating temps made these systems much more efficient, 30% more so. Even as the MOD-CONs became popular, we didn't use them. I worked for my brother, he doesn't like using new stuff until it is tried and trued by other people.

I am not disagreeing with you, since I don't have enough knowledge to know what I am talking about, just relaying what I have always been told.

 

[ewdudley]

Now if the emitters are sufficient to allow lower operating temperatures, what is the most economical way of lowering the storage temperature from say 190* to 150*?
I know this can be done with lots of money, but many of us are in this to save money.

If your system is compatible, then sdrobertson's variable-speed constant-temperature pump above would do the job nicely.

There's a sensor that you put in the return line to storage and the flow is slowed down or sped up to maintain the temperature you set it for. If you set it too low the pump runs slowly all the time and your house never quite gets warm enough, but you will have milked storage for all it's worth. Set it too high and you return water somewhat hotter than necessary to storage, no big deal. Down they road you could get a Tekmar control for it and the control will optimize for you.

I say if your system is compatible because if your baseboard is all one big loop then the beginning of the loop will be quite hot and the end of the loop won't be so hot. This may or may not matter depending on how your house works. If you have multiple circuits in parallel (regardless of the number of control zones) then having one end of each circuit significantly hotter probably wouldn't matter so much.

Alternatively, if you'd like to consider the diverter valve technique without springing for a Termovar or Danfoss; if your system can get by with five to six gpm total and a heat load of about 75000 btu per hour max with a system temperature drop of no less than 30 degF or so, then a $100 Taco 5000 valve could work as a diverting valve.

--ewd

 

[chuck172]

How about the tekmar 712:
http://tekmarcontrols.com/accessories/712.html

What about the taco delta t pump?

 

[Jeff S]

How does the Tekmar 712 mixing valve, (http://tekmarcontrols.com/accessories/712.html) differ from the diverter valve that Tarm sells? Don't both of them re-circulate return water back into the supply to lower emitter water temperatures? How about the delta t pumps? Wouldn't just slowing down the pump speed through the system do the same thing?
Jeff, do you feel that your 660 gallons of storage lasts longer with usable temps of 100-125* than it would at 160-190*?

Well Chuck you are talking usable temps that are approximately 60* lower
60* x 660gallons x 8.33 lb per gal = 329,868 more BTU's of useful storage.