Heating with Thermal Storage and Low Flow Temps

[maple1]

It sure would be helpful for one of the "engineers" to Explain the how's and whys of outdoor reset with indoor feedback with respect to being drawn from storage, system requirements ect. If John can run his house down to the stick your finger in it temps, as I have witnessed, I'm all ears for some real information. For me, I'm expanding on radiation to lower system temp requirements and flow then install odr with indoor feedback

What do you have now for radiation? And wondering if you've tried letting storage temps drop until your house starts losing temp to see what that point really is for your situation? (Might have to do that multiple times to get a better idea where that point is). It was a gradual thing for me, getting to the lows I see now.

I have an iron ring on my finger & degree on my wall, but it had nothing to do with this stuff, and I steered a slightly different course so don't have a stamp to go with it anyway. So afraid I'm out for that - lol.

 

[TCaldwell]

Maple, your a "engineer"

 

[velvetfoot]

I are too a engineer.

 

[Woodfarmer1]

Well I'm not an engineer, so John in laymans terms could you explain the shunt valve and do you need a controller or software for it to work. I seem to need as much heat as I can get to keep my temperatures up. I would love to heat my house on a steady diet of 100* water, but similar to maple the variables around here seem too much.
I built a timber frame with sip panels and it should be sealed up tighter than a popcorn fart, but when the wind howls it seems to come right through the walls, all my big windows probably don't help either

 

[JohnDolz]

Well I'm not an engineer, so John in laymans terms could you explain the shunt valve and do you need a controller or software for it to work. I seem to need as much heat as I can get to keep my temperatures up. I would love to heat my house on a steady diet of 100* water, but similar to maple the variables around here seem too much.
I built a timber frame with sip panels and it should be sealed up tighter than a popcorn fart, but when the wind howls it seems to come right through the walls, all my big windows probably don't help either

I am far from an engineer and can barely handle Laymans terms but let me try.

The shunt valve is just a mixing valve. Water from the top of the tank comes in 1 side. Water from the supply return comes in the other side and a diverter valve opens/closes to mix the 2 supplies to get the idea temp. I have a circulator pump in front of the valve "pulling" the 2 water supplies through the valve.

1. Yes you need a controller
2. It takes in 2 readings (lets forget about my 3rd/Indoor reading for now)
a. Outdoor Reset provides outdoor temp
b. a temperature sensor is strapped to my flow pipe just before it goes into the manifold
3. Based on the Outdoor temperature the controller chooses the ideal temperature of the flow water (see photo of heat curve) - heat curves are a function of the controller
4. The controller then adjusts the shunt/mixing valve accordingly (opening to let in more hot water from the top of the tank or closing to cause more return water to be mixed in) to hit the target temperature identified on the heat curve. The controller keeps reading the 2 temps )outdoor and flow) and keeps adjusting accordingly. Things probably function a little smoother in Europe because they don't have o many zones. My return temp varies as zones kick on and ff. When my Modine Hydronic Heater kicks on you can almost see ice cubes coming back into the return (I am starting with such low water temp that once that big blower fan gets done with it there is nothing left in the return).
5. Ideally your thermostats will be in a constant call for heat and the temperature will e exactly where you want it due to the water temperature.

Like you I have a lot of glass so I do have different parts of the house heating up differently. Interestingly in the shoulder seasons it seems like the areas with the glass are the hottest (easiest to heat); once it get cold this reverses and the "glass" zones become the toughest to heat. Hope this helps. I'd be happy to jump on a call if I have done nothing but confuse you.

As you can see above there is room for improvement but at some point (if I chase every efficiency opportunity) it will be cheaper for me just too build a new house.

 

[Woodfarmer1]

Fisrst entering the basement from my garn is the water hx for domestic hot water.
I have my rads plumbed into my primary with a gate valve to adjust flow to the rest of the system ( I run the primary pump 24/7 on high.)
My basement loop in slab comes next, closely spaced tee with its own pump on high with its own thermostat and mixing valve. Which I have turned on in anticipation of the cold snap to come Sunday for the next week. I still am not sure if it stores enough heat to be worthwhile as it does use a fair bit of the storage.
Then my main floor loop in floor joist also closely spaced tee with its own pump on high and thermostat which I also leave on 24/7. Then the expansion tank and primary pump, which pulls through my system and pushing the water from this point back out to the garn water hx.
I'm open to recommendations for any efficiencies?

 

[maple1]

Fisrst entering the basement from my garn is the water hx for domestic hot water.
I have my rads plumbed into my primary with a gate valve to adjust flow to the rest of the system ( I run the primary pump 24/7 on high.)
My basement loop in slab comes next, closely spaced tee with its own pump on high with its own thermostat and mixing valve. Which I have turned on in anticipation of the cold snap to come Sunday for the next week. I still am not sure if it stores enough heat to be worthwhile as it does use a fair bit of the storage.
Then my main floor loop in floor joist also closely spaced tee with its own pump on high and thermostat which I also leave on 24/7. Then the expansion tank and primary pump, which pulls through my system and pushing the water from this point back out to the garn water hx.
I'm open to recommendations for any efficiencies?

Sounds like all your pumps are on 'high'. No idea what that translates to GPMs, but have you ever measured (accurately) all your in & out temps to see what your dTs are everywhere? Just wondering if you can lower your flows any to try to improve things. Or if you're observing any performance lows of some sort.

 

[JohnDolz]

Sounds like all your pumps are on 'high'. No idea what that translates to GPMs, but have you ever measured (accurately) all your in & out temps to see what your dTs are everywhere? Just wondering if you can lower your flows any to try to improve things. Or if you're observing any performance lows of some sort.

i used the VERY unscientific approach of asking "doesn't slowing down flow do about the same as adding more emitters?". My "gut check" conclusion was yes so all of my pumps are on the lowest speed. No idea if it is correct and I am sure I have horrified many here that put so much thought and research into things but it works for me.

 

[JohnDolz]

Well I'm not an engineer, so John in laymans terms could you explain the shunt valve and do you need a controller or software for it to work. I seem to need as much heat as I can get to keep my temperatures up. I would love to heat my house on a steady diet of 100* water, but similar to maple the variables around here seem too much.
I built a timber frame with sip panels and it should be sealed up tighter than a popcorn fart, but when the wind howls it seems to come right through the walls, all my big windows probably don't help either

Since it is a cold rainy morning I thought letting you see what the last 24 hours looked like in this environment:

1. I knew it wasn't going to be very cold so I did not max out the boiler on the last burn
2. As you can see on the shunt motor the knob is in the 1/2 way position - I still have a way to go
3. The "spikes" in the flow temperature are when my propane kicks in for DHW. This will be replumbed in the spring so that storage is heating DHW most of the time.
4. The big dip in flow temp is when I drop into energy Saver mode from 7:00 PM - 3:00 AM
5. You can see that the only time my flow water was over 50C in the last 24 hours was at 3:00 AM when my house started its recovery from setback, it then started adjusting downwards as actual room temperature got closer to target temperature. The exception to this are the spikes caused by the call for DHW (described in #3 above).
5. Bottom line is that my house has recovered to 72F and is staying there using 105F Degree water

 

[velvetfoot]

What is interesting to me are the spikes in flow temperature, like an on/off kind of thing with a differential. I would've thought mixing valve control would've been smoother, but I have no experience in this.

 

[JohnDolz]

What is interesting to me are the spikes in flow temperature, like an on/off kind of thing with a differential. I would've thought mixing valve control would've been smoother, but I have no experience in this.

I agree, I think Tom C had a thought on that (the type of device making the adjustment) - I will send him a note and ask him to weigh in. The other thought I have is that these systems are designed for a European environment. My understanding is that they do not have thermostats and cirulator pumps. Instead they have a pump (they call is a radiator pump) that pushes water through the whole loop (sometimes 2 loops in a bigger house but the Effecta can drive multiple shunt valves). The end result of this is that they have constant temp on the return water. In my environment I have circulators kicking on and off (plus the DHW spike) that change the temp of the return water. I have a big Modine Hydronic heater in my basement, when that thing kicks on it returns ice cubes into the return line. I'm thinking that this causes my controller to keep chasing ideal temps. I am open to other thoughts.

Tom what do you think?

 

[velvetfoot]

What does the 40(41) mean? It sort of implies a differential around a set point?

 

[JohnDolz]

What does the 40(41) mean? It sort of implies a differential around a set point?

The (41) is the target temp based on the outdoor temp. The 40 is the actual temp.

 

[JohnDolz]

I agree, I think Tom C had a thought on that (the type of device making the adjustment) - I will send him a note and ask him to weigh in. The other thought I have is that these systems are designed for a European environment. My understanding is that they do not have thermostats and cirulator pumps. Instead they have a pump (they call is a radiator pump) that pushes water through the whole loop (sometimes 2 loops in a bigger house but the Effecta can drive multiple shunt valves). The end result of this is that they have constant temp on the return water. In my environment I have circulators kicking on and off (plus the DHW spike) that change the temp of the return water. I have a big Modine Hydronic heater in my basement, when that thing kicks on it returns ice cubes into the return line. I'm thinking that this causes my controller to keep chasing ideal temps. I am open to other thoughts.

Tom what do you think?

Just thinking about this and would like to take back my comments on the theory of circulator pumps. Since all my zones would be in constant call during recovery the return temp should be pretty constant (trending up) so I imagine it is either how the motor works or how the programming was done. In theory my pumps should always be on but in reality that is not the case.

 

[DBoon]

I changed my habits last year as I also read then observed first hand that lower temps = less wood burned. I don't do any mixing though, I just deplete my storage before I burn. Depleted = when the house can no longer maintain temp.

I've been following various threads in this topic and my main question has been whether John's system is just one result that could be obtained or if another, equivalent result could be obtained through the following:

1. Install TRVs on cast iron radiators that have sufficient size to heat at water temperatures in the 100-120 degree F range (120 degrees needed for a 0 degree outdoor day, 100 degrees ok for a 40 degree outdoor day)
2. Install a constant pressure pump to circulate water from boiler storage
3. Charge storage when water temps are ~100 degrees F up to ~180 degrees F

That seems to be Maple1's approach, and simpler with less control complexity and "things that can go wrong". What am I missing?

 

[JohnDolz]

I've been following various threads in this topic and my main question has been whether John's system is just one result that could be obtained or if another, equivalent result could be obtained through the following:

1. Install TRVs on cast iron radiators that have sufficient size to heat at water temperatures in the 100-120 degree F range (120 degrees needed for a 0 degree outdoor day, 100 degrees ok for a 40 degree outdoor day)
2. Install a constant pressure pump to circulate water from boiler storage
3. Charge storage when water temps are ~100 degrees F up to ~180 degrees F

That seems to be Maple1's approach, and simpler with less control complexity and "things that can go wrong". What am I missing?

If you are talking about not mixing water and just puling from the top of the tank I would refer back to the post I wrote referring to using "cruise control" in a car. You will loose the extra mileage you can get via mixing and being really stingy with your water. If what you are talking about is simply running temperature down in the storage, you might gain some efficiencies on the lower end but mainly I think you are just stretching time between firings.

 

[DBoon]

Well, I'm not looking for analogies, I'm looking for some sort of technical detail. But here is what I think you are advocating - If a TRV on a radiator in a room opens, and a constant pressure pump pumping from the top of the tank pushes water to the radiator until it gets warm enough to close the TRV valve, the downside is that it is not sensitive to outdoor temperatures - it might push too hot water to the radiator and overshoot the desired temperature a bit. I think what you are advocating is an outdoor reset control, and the benefit of efficiency comes with the outdoor reset, and a mixing valve on the storage output is used in conjunction with an outdoor reset to ensure that the water temperature is only what is needed. Is that correct?

 

[JohnDolz]

Well, I'm not looking for analogies, I'm looking for some sort of technical detail. But here is what I think you are advocating - If a TRV on a radiator in a room opens, and a constant pressure pump pumping from the top of the tank pushes water to the radiator until it gets warm enough to close the TRV valve, the downside is that it is not sensitive to outdoor temperatures - it might push too hot water to the radiator and overshoot the desired temperature a bit. I think what you are advocating is an outdoor reset control, and the benefit of efficiency comes with the outdoor reset, and a mixing valve on the storage output is used in conjunction with an outdoor reset to ensure that the water temperature is only what is needed. Is that correct?

Correct. I will leave it to the Engineers to validate the math/provide technical data (I did go to RPI but I played football and was a Management Major). I never did the math behind using cruise control but I trust when I am told that it results in better overall gas mileage. I can tell you from personal experience that I can heat for longer periods of time on the same amount of BTU's in my tanks.

 

[JohnDolz]

Well, I'm not looking for analogies, I'm looking for some sort of technical detail. But here is what I think you are advocating - If a TRV on a radiator in a room opens, and a constant pressure pump pumping from the top of the tank pushes water to the radiator until it gets warm enough to close the TRV valve, the downside is that it is not sensitive to outdoor temperatures - it might push too hot water to the radiator and overshoot the desired temperature a bit. I think what you are advocating is an outdoor reset control, and the benefit of efficiency comes with the outdoor reset, and a mixing valve on the storage output is used in conjunction with an outdoor reset to ensure that the water temperature is only what is needed. Is that correct?

Also as you are doing your research you can look into high efficiency condensing gas boilers. I learned that they get their high efficiency ratings when they are firing at very low temperatures. Mine is rated 95% Efficient and that # comes with 140F Supply and 120F Return (not sure if those are the temps that all boilers are tested/rated at). If I understood what I read correctly, condensing boilers will only condense (and therefore be really efficient) when return water is 120 or less. My propane boiler (Triangle Tube) is designed in Belgium, designed to use an Outdoor reset and follow a heat curve (you have the ability to move the endpoints around and then it is linear). I didn't know anything about this when it was installed (just followed my plumbers recommendation) and it was installed with a fixed firing point of 180 so it never actually condensed. Long story to be told over a coffee but again it is the same theory of efficiency gained at low temps. Hope this helps.

 

[TCaldwell]

It was explained to me that, if baseboards flow is too low it will stratify in the pipe, causing cooler spots in the fin tube. This isn't the case with radiators as they will eventually homogenize in temp.
in my humble opinion trv's with radiators with outdoor reset, with system running all the time would be hard to beat, you could have lower flows resulting in longer storage drawdown. However john's system is case in point for outdoor reset with indoor feedback, even with fin tube.
I've looked for empirical data on odr, not able to find much other than not having to play thermostat catchup 20 or so times a day and matching load with demand only supplying what's needed. I guess it is possible this can add up!
The temp spikes or oscillations around design water temp set point are a result of floating point control that is employed with most odr equipt manufacturers. This is not as stable as proportional control but widely used, the controller probably filters/averages these oscillations to arrive at a stable reading.
A better approach than running the garn circ 24/7 would be to use the end switch from your zone box and tie it to a single zone relay box that will energize the garn circ whenever a zone calls

 

[JohnDolz]

It was explained to me that, if baseboards flow is too low it will stratify in the pipe, causing cooler spots in the fin tube. This isn't the case with radiators as they will eventually homogenize in temp.
in my humble opinion trv's with radiators with outdoor reset, with system running all the time would be hard to beat, you could have lower flows resulting in longer storage drawdown. However john's system is case in point for outdoor reset with indoor feedback, even with fin tube.
I've looked for empirical data on odr, not able to find much other than not having to play thermostat catchup 20 or so times a day and matching load with demand only supplying what's needed. I guess it is possible this can add up!
The temp spikes or oscillations around design water temp set point are a result of floating point control that is employed with most odr equipt manufacturers. This is not as stable as proportional control but widely used, the controller probably filters/averages these oscillations to arrive at a stable reading.
A better approach than running the garn circ 24/7 would be to use the end switch from your zone box and tie it to a single zone relay box that will energize the garn circ whenever a zone calls

Thanks for the info Tom. Once again exposing my ignorance I had to go to Youtube to learn what TRV's are/do. After taking a look I would agree, running low temperature flow water that is then leveraged on a radiator by radiator basis would seem to get you everything you could get per BTU. One thought though is you could potentially drive yourself crazy trying to find the sweet spot between the TRV settings and the right heat curve. As far as stratification within the pipe, I've never noticed any cool spots but honestly never thought about it.

 

[TCaldwell]

The low flow that can stratify for fin tube is anything much less than a gallon per minute, I believe you have taco 3 speeds, if they are comparable to a grundfos 15-58 3 sp, speed 1 i was getting 2 to 4.5 gpm per zone, no stratification worry there.

 

[JohnDolz]

T

The low flow that can stratify for fin tube is anything much less than a gallon per minute, I believe you have taco 3 speeds, if they are comparable to a grundfos 15-58 3 sp, speed 1 i was getting 2 to 4.5 gpm per zone, no stratification worry there.

Thank you sir!

 

[Woodfarmer1]

My trv's are all the way open, as I need all the heat I can get out of them.

 

[DBoon]

Correct.

Thanks for this confirmation - that is what I surmised. Regarding the high efficiencies of condensing boilers, this is basically due to the capture of the latent heat in the flue gas as it condenses to liquid, and the low return temperatures are what makes this possible. Then, ODR with a mixing valve and flow control provides benefits in maintaining the storage tank thermocline, which I can easily buy into as well.

trv's with radiators with outdoor reset, with system running all the time would be hard to beat, you could have lower flows resulting in longer storage drawdown.

That's pretty much my thoughts. I'm lucky that I can design from the ground up and don't have to work with an existing system (i.e. fin-tube radiators), which would restrict my strategies somewhat and may require more complex control schemes.

I've looked for empirical data on odr

Yeah, me too. But I can believe that it can save money in some cases. For instance, my cast iron radiator system has two zones, and one of the thermostats turns on at set temperature and off at set temperature +4 degrees. If the temperature is warm, the cast iron radiators will take a while to heat up, and then once the temperature heat +4 degrees, and the boiler goes off, the room temperature will keep rising if the outdoor temperature is not too high. ODR senses that and keeps the boiler water output temperature lower to prevent unnecessary overshoot and unnecessary heating.