How Is Input Temp to Emitter Loop Controlled?

[velvetfoot]

I have a reset control with my oil-fired boiler that lowers output temp when outdoor temp is high (and vice versa). The idea being that boiler efficiency at lower temperatures. Is there an analogue for a gasifier with storage? For instance, the tank is fully charged, and conditions are right for 120F input water to the loop: would it pay to reduce the input to the emitters (somehow) to 120? How would one do this anyway, if it were indeed advisable and possible?

Or, would tapping into the hottest water from the tank and turning a circulating pump on and off periodically do it? Or, with some special pump that runs all the time that modulates, or something along that line. Until the tank extraction point temp got down to the lowest useable temp.

I'm sure this has been discussed already, somewhere. I'll keep reading.

 

[Clarkbug]

User Floydian has some good details about his setup. He uses a Taco iValve to mix down the temps coming out of storage based on the outdoor air temps. An alpha pump runs continuously, and each circuit has a non-electric t-stat with a capillary tube to control flow. Im jealous of how simple/effective it is.

Other ways to skin the cat, but thats a simple, easy solution.

 

[velvetfoot]

Where do you get the cooler water to mix with the hot?

 

[Willman]

from the return water

 

[__dan]

I have a reset control with my oil-fired boiler that lowers output temp when outdoor temp is high (and vice versa). The idea being that boiler efficiency at lower temperatures. Is there an analogue for a gasifier with storage? For instance, the tank is fully charged, and conditions are right for 120F input water to the loop: would it pay to reduce the input to the emitters (somehow) to 120? How would one do this anyway, if it were indeed advisable and possible?

Or, would tapping into the hottest water from the tank and turning a circulating pump on and off periodically do it? Or, with some special pump that runs all the time that modulates, or something along that line. Until the tank extraction point temp got down to the lowest useable temp.

I'm sure this has been discussed already, somewhere. I'll keep reading.

If the boiler reset control has direct control over the boiler firing, it will have to be setup to maintain above 140 deg F boiler return water temp to prevent flue gas condensation inside the boiler. It will give you a reset HWS temp, but in the range of 140 to 180 deg F and not lower (assuming the oil boiler is not condensing rated).

The question you're asking about is reset control over the load supply temp. Typically you would have a primary secondary pumped loops. The primary loop is the higher boiler water temp. The secondary loop temp is reset controlled using a variable speed injection pump or a motorized three way valve. That way the load loop temp may be any temp, independent of the boiler loop temp to prevent flue gas condensing.

 

[velvetfoot]

It really can't be just any temperature, though, can it? What if you're targeting is 120 and your storage is fully charged to what, 185 at the top and, I don't know 165 at bottom? You can't blend to a 120 target, can you? If there was a drop of 20 degrees, and you'd be starting at even 165, you could only get down to 145.

 

[Floydian]

Hi velvetfoot,

What if you're targeting is 120 and your storage is fully charged to what, 185 at the top and, I don't know 165 at bottom? You can't blend to a 120 target, can you?

You sure can but keep in mind we are mixing down the supply temp with the return of the heating side, not the boiler return from storage. He is a pic to give you better idea.
In my system the boiler only heats storage and I typically charge my storage to 175. My supply temps for my in floor heat ranges from mid 90's to 120 at my outdoor design temp ( 0) and I see a consistent 20 temp drop ( T)across my radiant floor.
Here you see the supply from storage for my heating system is on the left. This comes off the top of storage where the hottest water is available and goes to the Taco ivalve(the 3 way mixing valve with green actuator). The ivalve mixes the return from the radiant floor with the supply from the top of storage to deliver whatever temp the system is calling for. There are two sensors telling the ivalve what to do-one tells the ivalve what the outdoor temp is and the other tells the ivalve what the supply temp is. The is outdoor reset (ODR) in a not shell and you can adjust the reset ratio on the ivalve based on what supply temps you need at a given outdoor temp.

This is but one way to use ODR but I think it is relevant to your question.
Hope this makes sense,

Noah

 

[velvetfoot]

Thanks Noah and _dan and William and Clarkbug. Eureka, I think I get it now. Let me talk this through. I am thinking low temperature baseboard like the Heating Edge, but that's probably irrelevant. If, for example, the baseboard is room temperature and there is a call for heat, that room temperature water from distribution return is mixed with just enough water from storage to bring it up to what the reset curve specifies. Am I right?

Now, the question is, is the reset worth it? The source, in my scenario, is a storage tank, not a fossil fuel boiler, so does it even pay? If my prospective new wood boiler was simply grafted in series onto the existing wood boiler with circ pumps on the return, with storage, boiler protection, etc, the circ pumps would pump whatever temp was available at the top of the storage tank and would turn off when their zone's thermostat was satisfied. The circ pumps would run longer and longer as storage got depleted, until either the oil boiler came on or the wood boiler was fired. What's so bad about that? I've heard that pumping away from the boiler is better than on the return, so that's one basic thing I guess. I can see there'd be less noise with the expanding baseboard. I can see where the temp could be controlled very precisely for greater comfort. I'm not so sure about electic savings because of the constant running pump vs. the cycling circ pumps.

I've been running the oil boiler this morning because I'm having a new flue put in as I type, and I thought it best not to have a fire going. I have to say, there are reasons for the historical switch to central heating!

 

[maple1]

Not sure this was said before or not - but I would highly recommend a VS circ such as the Grundfos Alpha for pumping your loads/zones.

 

[jeffesonm]

That all sounds right to me, and I thought through many of the same considerations. The only tradeoffs I see are an evenness of temperature with constant circulation, vs marginal cost savings with cycling the pump. I say marginal because if you use a variable speed ECM pump, the difference between running all the time vs cycling is $2/month or even less.



I like the simplicity of ODR and constant circulation so that's what I'm planning. I will also tie the load circulator into the thermostat so it runs when there's a call for heat. I will target the ODR curve so at 68 on the thermostats, it runs at constant circulation. If I go away for the weekend and set back the thermostat to 55, it will cycle. I figure it's easier to adjust thermostats than adjust the reset curve.

 

[velvetfoot]

Not sure this was said before or not - but I would highly recommend a VS circ such as the Grundfos Alpha for pumping your loads/zones

Practically speaking, I'm going to be using baseboard with two zones. How would this pump be used then? One pump and two valves? What are the advantages of the variable speed pump in distribution? Would this pump be running all the time?

 

[velvetfoot]

I like the simplicity of ODR and constant circulation so that's what I'm planning. I will also tie the load circulator into the thermostat so it runs when there's a call for heat. I will target the ODR curve so at 68 on the thermostats, it runs at constant circulation. If I go away for the weekend and set back the thermostat to 55, it will cycle. I figure it's easier to adjust thermostats than adjust the reset curve.

Jeff, are you running baseboard or radiant? How are the temperatures for each room controlled, assuming you might want different temperatures for say, upstairs and downstairs? I still have much to understand.

 

[jeffesonm]

Baseboard. I have two zones now but I'm going to drop the zone valves and just run it all as one.... the floor plan is pretty open and we use most of rooms regularly so it's not worth the trouble of zoning it. I plan to keep the bedrooms at the end of their respective loops so they stay a bit cooler.

 

[Clarkbug]

Practically speaking, I'm going to be using baseboard with two zones. How would this pump be used then? One pump and two valves? What are the advantages of the variable speed pump in distribution? Would this pump be running all the time?

I have that same setup. Two zones, both baseboard. I have two circs, taco zone control, pretty simple. To use a variable circ, you would want to use one pump, then use zone valves. If you want to vary the temp, you would use the variable pump, a reset valve, and zone valves.

I have a valve on the return to my storage that is a thermostatic valve. If the water temps are too high, it goes back around the loop again. If its cold, it goes to the bottom of storage. (Its whats called out in the Tarm piping diagrams). Simple, no power, works. But it does make the pipes sing when storage gets cold, and that bums me out.

 

[velvetfoot]

To use a variable circ, you would want to use one pump, then use zone valves. If you want to vary the temp, you would use the variable pump, a reset valve, and zone valves.

Still not sure about the variable circ pump. If I would use one, it would cycle off if no zone called for heat and vary it's output depending on how many zones called for heat?

I have to study.

 

[Clarkbug]

Well, it depends on how you have your existing controls set up. For instance, I have a Taco zone controller hooked to the oil boiler. If you had one set up for use with zone valves, any time there was a call for heat, the pump would be on, and it would vary its output depending on how many zones were open (when running in constant pressure mode). Ill be the first to admit with just two zones and zone valves, its probably not the best use of a variable speed pump. They really shine when you have multiple circuits.

 

[timberr]

I am using a re-set controller (Tekmar 260) and it is pretty simple. I am running primary/secondary setup. I have a temp sensor at the input of the circ on my primary loop which is connected to the 260. When there is a call for heat the Tekmar determines the target temp given the outside temp. The circ on storage is turned on as storage water enters from the injection side the temp climbs when the temp get's 2* above the target (2* delta is set) the circ on storage turns off, the circ on the primary continues to circulate water to the zone, when the water get's 2* below the target the circ on storage starts again injecting hot water until it climbs above, on and on until the zone is satisfied.

 

[velvetfoot]

I am using a re-set controller (Tekmar 260) and it is pretty simple. I am running primary/secondary setup. I have a temp sensor at the input of the circ on my primary loop which is connected to the 260. When there is a call for heat the Tekmar determines the target temp given the outside temp. The circ on storage is turned on as storage water enters from the injection side the temp climbs when the temp get's 2* above the target (2* delta is set) the circ on storage turns off, the circ on the primary continues to circulate water to the zone, when the water get's 2* below the target the circ on storage starts again injecting hot water until it climbs above, on and on until the zone is satisfied.

What is the advantage of reset when using heat from storage. At a lower water temperature, wouldn't the pumps have to run longer to satisfy the thermostat? There's a fixed amount of heat stored in the tank-I can't see how removing it at a lower rate for a longer time makes any difference.

 

[ewdudley]

What is the advantage of reset when using heat from storage. At a lower water temperature, wouldn't the pumps have to run longer to satisfy the thermostat? There's a fixed amount of heat stored in the tank-I can't see how removing it at a lower rate for a longer time makes any difference.

[Edit: This following is complete nonsense.]

For baseboard you're right, if you're heating storage to a relatively high temperature what's the difference between running hot water twenty percent of the time vs. not so hot water all the time so long as all zones are at setpoint? Except with wood boilers and storage there's a need to minimize return temperature to storage in order to maximize the storage capacity, and reset systems achieve this.

Reset systems are usually designed to increase efficiency by using the lowest possible supply temperature from a gas, oil, or heat pump heat source, but it turns out they work well for maximizing storage capacity in a wood boiler with storage system. With low-power constant-pressure ECM pumps (ECOCIRC, Stratos, Alpha ...), the cost of running the heat distribution pump nearly all the time becomes a small price to pay.

 

[timberr]

Thanks edudley for jumping in and answering for me. I wish I had a way of timing the amount of time the Primary & Storage circ run so I could see how my temp selections on the Reset control affect thier running time. All I know is when I first setup my system I would get home the house was cold, both my circ's were running and storage 140 or less and I would struggle to get the house & storage up to temp for a couple of hours. Know I come home, house is warm, storage is adequate, I fire the boiler up and by the time I go to bed storage is charged for the night. If you want to stretch storage you have to make compromises else where, I use a little more electricity.

Good luck

 

[velvetfoot]

I still don't understand, but I'll take your word for it.

But.... If no reset and the hottest storage temp circulated though distribution, the on time of the distribution pumps would increase as storage temp went down. You're still going down to the storsage temp point where the space heat loss exceeds gain. I still can't see where the reset way would consume energy at a lower rate.

I'll do some more reading. Sorry to be a dumb ass.

 

[ewdudley]

I still don't understand, but I'll take your word for it.
But.... If no reset and the hottest storage temp circulated though distribution, the on time of the distribution pumps would increase as storage temp went down. You're still going down to the storsage temp point where the space heat loss exceeds gain. I still can't see where the reset way would consume energy at a lower rate.

I wasn't saying that energy was consumed at a lower rate, I was saying that more total energy could be pulled out of storage because the ending temperature of storage would be lower if emitter temperature is as low as possible while still meeting demand. If tank starts out at 180 degF and ends up at 130 degF as opposed to ending up at 140 degF then storage lasts longer (and will take more heat to bring back up to 180 degF).

That's the theory anyways. I just ran the numbers and you are correct. Lowering the temperature going into the emitters exactly to the point where the emitter pump has to run 100% of the time does not somehow magically lower the final temperature of the storage tank. Sorry to be a dumbass!

 

[velvetfoot]

I'd just like to say that I'm more the dumbass.

I'd also like to say that I'll only replace the current baseboards for high performance units AFTER the boiler is installed and running for a time.
And, furthermore, radiant floors are not in my future.