For you control freaks :)

[heaterman]

Here's a little info from Taco on Delta T vs Delta P circulators. Each have their merits and this article is a little slanted toward the Taco "way" but it contains a lot of good info. Just thought I'd share. An educated customer is my best customer.

http://www.taco-hvac.com/images/vdt_resources/WhitePaper_00VDT_DT_DP.pdf

 

[Nofossil]

Good paper, but most of the basis for their whole discussion goes out the window if you have storage.

My current thinking is that varying flow rates to achieve selected temperature targets is the right way to go, especially if you can adjust the temperature targets based on current circumstances. They're right that running the boiler with the coldest possible water (inlet and outlet) gives better efficiency. With ours we need to avoid condensation, but beyond that colder is better. In my current setup (with my 'poor mans variable speed circulator'), I juggle loads and flow rates to keep the boiler outlet at the lowest temp that will do the job. Baseboards and near-full storage needs high temps, but nothing else does.

 

[chuck172]

"Good paper, but most of the basis for their whole discussion goes out the window if you have storage."

Could you go into a little more detail on using a delta t variable circulator as the heating load circulator in your " Simplest Pressurized Storage System Design"
It would seem to me that throttling the speed of this circulator, sending the required btu's with a 20* delta T to the heating zones and automatically dumping the rest into storage would be the cat's meow!

 

[Nofossil]

"Good paper, but most of the basis for their whole discussion goes out the window if you have storage."

Could you go into a little more detail on using a delta t variable circulator as the heating load circulator in your " Simplest Pressurized Storage System Design"
It would seem to me that throttling the speed of this circulator, sending the required btu's with a 20* delta T to the heating zones and automatically dumping the rest into storage would be the cat's meow!

Keep in mind that I'm making this up as I go along...

My thinking is that ideal operation occurs when the flow rate through the loads is matched to the heat demand. At the simplest level, it should be proportional to the number of zones calling for heat. You probably could go farther and reduce the flow rate a bit if the heat load per zone is lower. You could determine that by seeing that the zones are close to their setpoint (or estimate load from outside temp). You can't go too far in that direction or the far end of each zone won't get enough heat, but lower flow rates would give you lower return temps. That's good for stratification.

Keep in mind that Taco and others make circulators designed for zone valve systems so that the total flow rate is roughly proportional to the number of open zone valves. What they do is design the zone valves so that the valve itself provides most of the head loss for the zone. In that way, two open zone valves present the circulator with a head loss that yields roughly twice the flow rate that you would get with only one zone valve open. It's rough, and it falls apart when you get beyond about four zone valves. Still, it fits the 'simplest' idea pretty well.

 

[chuck172]

"lower flow rates would give you lower return temps. That’s good for stratification."
Then when heating from storage, would a three speed pump set at the lowest level be best for the heating zone pump?
The pump would return to storage the cooler, less turbulant hot water.

 

[Nofossil]

"lower flow rates would give you lower return temps. That’s good for stratification."
Then when heating from storage, would a three speed pump set at the lowest level be best for the heating zone pump?
The pump would return to storage the cooler, less turbulant hot water.

More importantly, the lower speed would result in lower return temps to storage. At some point, you're not getting enough heat out of the system, but ideally you'd want to be as close to that point as you can get.

In fact, I'm planning to set up my radiant zone so that it uses return water from the baseboard zones as its hot supply, allowing me to extract more heat before returning the water to storage.

 

[kabbott]

"lower flow rates would give you lower return temps. That’s good for stratification."
Then when heating from storage, would a three speed pump set at the lowest level be best for the heating zone pump?
The pump would return to storage the cooler, less turbulant hot water.

More importantly, the lower speed would result in lower return temps to storage. At some point, you're not getting enough heat out of the system, but ideally you'd want to be as close to that point as you can get.

In fact, I'm planning to set up my radiant zone so that it uses return water from the baseboard zones as its hot supply, allowing me to extract more heat before returning the water to storage.

I would agree with Nofo on this point. I have seen this in my own system, stratification varies wildly depending on boiler input/load return temps
and the pump speed I select. I use 2 taco 00R pumps back to back and PEX coil for my storage and generally the slower the better as long as it
can keep up.

 

[chuck172]

I kept the load circ. on low last night, also re-circulated the return through the finned tube radiation to get lower back- to-tank return temperatures. It seemed to make a difference. Much better stratification. Thanks

 

[pybyr]

"lower flow rates would give you lower return temps. That’s good for stratification."
Then when heating from storage, would a three speed pump set at the lowest level be best for the heating zone pump?
The pump would return to storage the cooler, less turbulant hot water.

More importantly, the lower speed would result in lower return temps to storage. At some point, you're not getting enough heat out of the system, but ideally you'd want to be as close to that point as you can get.

In fact, I'm planning to set up my radiant zone so that it uses return water from the baseboard zones as its hot supply, allowing me to extract more heat before returning the water to storage.

No BTUs Left Behind @ Nofossil's!