can one circulator be used with 1-zone valve and DWH priority?

ron · April 19

reference thread sort of : https://forum.heatinghelp.com/discussion/188062/one-circulator-and-using-zone-valve-for-dwh-indirect-pic#latest

with an oil boiler and indirect hot water heater and 1 zone of baseboard heating, can one [delta-T] circulator be used along with 1 zone valve [3-way?] such that if the one zone of baseboard heat is calling then if the hot water heater calls (i.e. 7am in winter for a shower) that the one zone valve stops the baseboard heat and runs the hot water heater?

Wondering if a setup of an oil boiler, and indirect dhw, only one [delta-t] circulator and only one zone valve is a possible setup {using a hydrostat 3250 for starters}. Thanks.

GGross · April 19

If you only have 1 circ, and 1 zone valve how do you stop flow to the indirect when it is not calling? I may just be getting hungry (lunch time) but it seems to me you will need to add another zone valve, or use 2 pumps

Labenaqui · April 19

Precisely what we've done in our patented delta-t heating appliance. Zone valves for heating zone(s) and IWH zone immediately above the VT2218 dedicated system circulator.
By further branching immediately above the circ and "close-coupling" your IWH to the lower boiler return tap you have a de facto priority loop. Even with a circ failure you never run out of DHW!

ron · April 19

that's why I was asking....

Thought was using one 3-way zone valve and one circulator. The normally-open (no-call) side of the 3-way zone valve would run the indirect so the indirect call for heat would only need to kick on the boiler and not operate a 3-way zone valve, but

When baseboard heat calls is would then override indirect (cancel dwh priority) and run the beaseboard zone.

So is there a way for when the indirect calls, to have dwh priority, to cancel the baseboard heat call to the zone valve so the zone valve goes back to no-call normally open?

being 20 years into the 21st century i sort of expect this to be possible given electronic this and transistor that

mattmia2 · April 19

You could do it with a 3 way valve maybe with a double throw end switch. Not sure why you would want to and you would have to be careful that the 3 way valve could provide correct flow to both zones. It would make a lot more sense to just use 2 zone valves. You may also need a flow check in the "off" position of the 3 way valve.

GGross · April 19

ron said:

being 20 years into the 21st century i sort of expect this to be possible given electronic this and transistor that

It's not a question of control capability, but rather water flow and expectation of system performance. Generally speaking we would design the system to run as much as possible while in space heating mode, with a priority on/off for DHW. What you have described is a priority space heating with DHW taking a backseat. Assuming that your set-up meets whatever flow requirements your boiler has, you have already described how to achieve what you are looking for.

Personally I am in total agreement with @mattmia2 on this. 2 zone valves, 1 circ, DHW on priority. If the boiler has not been purchased yet I would be looking at whether or not a combi would be a good fit for the application, I would wager a guess if the current plan is to set space heating to priority that you have very little DHW needs.

ron · April 19

sorry but what is a "combi" ?
Are there oil-fired combi's?
Because I am stuck with oil, at best I could do propane but have already determined it would be more expensive to heat with propane than oil. All I am aware of are condensing gas/propane boilers at high 90% efficiency which I am not willing to do for (a) upfront cost and (b) acidic condensate and septic system. So for part cost a cast iron regular boiler is what I am planning on.

https://selectra.ie/energy/guides/boilers/combi-boiler

A combi boiler (also known as a combination boiler) provides both hot water and heating from one single unit. A combi boiler is linked to your mains water supply and the water is heated as it passes through the boiler. This allows you to have hot water as soon as you turn on the tap (or in about 20 seconds).

a tankless like a weil wtgo versus wgo? can someone write or pic technical stuff so i can understand whatever combi is supposed to mean? And tell me of a specific make and model of combi boiler that I can reference.

I was reading taco 3-way zone valve description and what I was hanging up on was their statement to wire & pipe the no-call side of the 3-way zone sentry to the circuit that will operate the most, which would be the indirect water heater. However to achieve dwh priority and using 1 circ and 1 3-way zone valve I would just need to make the dwh run on the call side of the zone valve, duh.

and if I didn't I suppose and wanted the DHW priority to interrupt the baseboard heat call and make the zone valve go to the no-call side I could use a $15 OONO DPST 1NO 1NC 8Amp Power Relay Module, AC/DC 24V Control Voltage.

The 1" piping taco 3-way valve has a stated 5 second activation time so if I did use the call side for it for DWH I figure that would be fine. My goal of all this was to use 1 circulator, preferably a delta-t, to operate both the indirect dwh and 1 zone of baseboard heat.

GGross · April 19

Specifically I was referring to a modulating condensing gas fired boiler that has a built in DHW circuit for on demand hot water(example of this would be Viessmann B1KE-120). I am not terribly familiar with oil fired appliances but there are cast iron boilers that offer a tankless coil, slant-fin intrepid is an oil fired cast iron boiler that offers a tankless dhw coil.

If it makes any difference the acidic condensate from a condensing gas appliance can be easily neutralized, manufactured ones are not terribly expensive, or you can make your own pretty easily. Condensate management should not be a deterrent from going condensing, but as you mentioned changing fuel types seems to be the biggest concern

Intrepid from slant fin
https://www.slantfin.com/products/intrepid-water-boiler/

Viessmann combi, this link also covers the heat only version which still has separate tappings for a DHW tank
https://www.viessmann-us.com/en/products/vitodens/vitodens-100-b1he.html

EBEBRATT-Ed · April 19

@ron

There is no magic to this of course it is easy to do but you may find two zone valve cheaper than 1 3 way valve.

you could use a NO valve for the indirect and a NC valve for heating. Power them both on a call for heat. Wire the end switch on the heating zone valve in parallel with the control on the indirect to fire the boiler and your done. No flow check valves needed

hot_rod · April 19

ron said:

sorry but what is a "combi" ? Are there oil-fired combi's? Because I am stuck with oil, at best I could do propane but have already determined it would be more expensive to heat with propane than oil. All I am aware of are condensing gas/propane boilers at high 90% efficiency which I am not willing to do for (a) upfront cost and (b) acidic condensate and septic system. So for part cost a cast iron regular boiler is what I am planning on. https://selectra.ie/energy/guides/boilers/combi-boiler
A combi boiler (also known as a combination boiler) provides both hot water and heating from one single unit. A combi boiler is linked to your mains water supply and the water is heated as it passes through the boiler. This allows you to have hot water as soon as you turn on the tap (or in about 20 seconds).
a tankless like a weil wtgo versus wgo? can someone write or pic technical stuff so i can understand whatever combi is supposed to mean? And tell me of a specific make and model of combi boiler that I can reference. I was reading taco 3-way zone valve description and what I was hanging up on was their statement to wire & pipe the no-call side of the 3-way zone sentry to the circuit that will operate the most, which would be the indirect water heater. However to achieve dwh priority and using 1 circ and 1 3-way zone valve I would just need to make the dwh run on the call side of the zone valve, duh. and if I didn't I suppose and wanted the DHW priority to interrupt the baseboard heat call and make the zone valve go to the no-call side I could use a $15 OONO DPST 1NO 1NC 8Amp Power Relay Module, AC/DC 24V Control Voltage. The 1" piping taco 3-way valve has a stated 5 second activation time so if I did use the call side for it for DWH I figure that would be fine. My goal of all this was to use 1 circulator, preferably a delta-t, to operate both the indirect dwh and 1 zone of baseboard heat.

Why would you want a delta t circ on an indirect? If you have a cold, hungary indirect load, and you will, why would you constrain it to a fixed delta? And would that fixed delta ever be correct for heating and DHW?

HVACNUT · April 20

Labenaqui said:

Precisely what we've done in our patented delta-t heating appliance. Zone valves for heating zone(s) and IWH zone immediately above the VT2218 dedicated system circulator. By further branching immediately above the circ and "close-coupling" your IWH to the lower boiler return tap you have a de facto priority loop. Even with a circ failure you never run out of DHW!

You gotta draw that one.

ron · April 20

Why would you want a delta t circ on an indirect? If you have a cold, hungary indirect load, and you will, why would you constrain it to a fixed delta? And would that fixed delta ever be correct for heating and DHW?

That was going to be one of my future questions. I don't know. Is it really a problem such that a dedicated circulator is needed to pump the indirect water tank circuit, which for a weil mclain aquaplus2 says 8 gpm recommended having 1.6 ft of head loss. So if a delta-t circ was left on 20°F delta in order to accommodate the baseboard heat zone how would that actually work if the 20°F delta-t setting was pumping from a WGO2 boiler fired at 0.7gph feeding a 35gal or 45gal indirect ?

If the indirect for example is newly filled with 40°F water and the boiler kicks on and the circulator runs in 20°F delta-t mode what is going to happen? Where on the pump curve is the cir going to operate? On the low end using low watts and pumping minimal gpm, or would it operate at its maximum? If the circ sees a high delta-t measurment do they try and pump less or more to reduce the delta? If it's less then that's bad for pumping to the indirect right?

can you ever pump to fast to an indirect, if so how likely or easy is it to happen?

A new boiler comes with a 007, so i don't really have a problem using a dedicated circ for the indirect, just mulling over possibilities of how the minimal amount of controls could be used.

hot_rod · April 20

The hotter the heat exchanger, heat emitter, the higher the heat transfer. Hot goes to cold, always. The rate of that transfer is based on the delta T.

So the flow limitation is flow velocity. CDA suggest 4 fps limitation in copper tube running 140 or warmer. That is mainly for DHW with fresh chlorinated water, closed loop Hydronics can run up to 5 fps in these intermittent load applications. The universal hydronic formula defines this 500 [flow] [delta t]

Lots of flow at high temperatures get you DHW the quickest, allowing you to get back to the heating loads.
Electrical consumption is less of an issue now with ECM circulators. As higher flows require more pumping energy.

In some cases if fast DHW recovery is not a priority, lower temperature SWT could allow a mod con to stay in condensing mode for best fuel efficiency. Lots of coil surface area also helps with that
Do you want DHW fast, most efficiently, or somewhere in the middle. Through the miracle of math you can get those answers.

But hurry if you are in Florida.

MikeAmann · April 21

ron said:
A new boiler comes with a 007, so i don't really have a problem using a dedicated circ for the indirect, just mulling over possibilities of how the minimal amount of controls could be used.

You are overcomplicating a simple situation.
Use the Delta-T for heat. Use the supplied Taco 007 for the indirect. Forget the 3-way valve.
Forget ANY valves. Both circulators already have built-in check valves.
The Hydrostat already is set up to give priority to the indirect. With a CFH, the indirect heats, then automatically goes back to heating the house.

I have an indirect diagram that uses a 3-way valve. I will post it late tonight for you.

I found a few diagrams:

can one circulator be used with 1-zone valve and DWH priority?

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