Crispy's old small house reno - questions about modifying existing zones

HeatingHelp

This discussion was created from comments split from: One circulator pump with 2 zone valves, or two circulator pumps?.

Crispy

I'm doing a very similar thing… I did a complete reno of an old but small house. I needed to get the system up fast before winter and before I really knew what I wanted. The downstairs (Zone 1) is 100% radiant floor heat, mixed down on its own zone. The upstairs (Zone 2) is 100% cast iron baseboard in three different rooms. For the cast iron, I came off the primary loop (unmixed) with a circulator and made little supply and return manifolds that are off to the side of everything else and have a branch going to each of the three rooms upstairs. I ran thermostats from each room to the basement but have been running off one room and just heating the whole upstairs from the one t-stat on Zone 2. It's been working fine but three years later, I want to fix it and have control for each room upstairs. Thinking zone valves off my little manifold. I read the responses above but have a question. Balancing issues aside, when one or more of the new zone valves fires for one of the three rooms upstairs, can I send that power to Zone 2 in the Taco zone controller? Put another way, can I have three different zone valves talking to one zone in the Taco controller? Thanks in advance, C.

HomerJSmith

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@dbarck2000, I would go with 3 pumps, a boiler pump and two zone pumps, but, you could go with two pumps and Zone valves. The zone pump would be a ECM pump. I would pipe pimary/secondary. I would use a Taco ZVC controller or a Caleffi ZVC. I would definitely use balancing valves for each apartment circuit.

If you circulate to the apartments with 2 zone pumps, use a relay pump controller.

mattmia2

Are you trying to control 3 zones with one t-stat or 3 zones with 3 t-stats? You can do either assuming that the zone controller can provide enough power for all 3 zone valves.

also be careful with making separate zones that are small compared to the output of the boiler, that will cause the boiler to short cycle it only one or maybe even 2 zone(s) is/are calling.

Crispy

Three zones with three stats. Thank you. Was planning to dedicate a new transformer for these three ZV's and this purpose so I should be able to size it to provide enough power. Good point about one small room calling. Is that where the variable speed pump described above comes in? I'm happy to invest in a fancy smart pump to accomplish this. C.

Crispy

Zone valves are new to me so I have been learning. It looked to me that the 24V power supply runs through the t-stats first and then on to the ZV's to run their heaters. The End Switch side of the ZV's isn't a consumer of power. If so, I can provide a robust 24V transformer to handle the load.

mattmia2

What kind of boiler is it? Is it a conventional CI boiler or a mod con? The problem comes in when the boiler is producing a lot more heat than the calling zone can absorb. A circulator can't fix that problem. A buffer tank or combining zones that have similar demands is the way to fix that.

You would power each zone valve and t-stat off the transformer then you would parallel the end switches on to the end switch terminals for that zone in the zone controller, that way when one or more of the end switches closes it will make a call for heat from the boiler.(if the transformer in the zone controller is big enough you could power it off the zone controller)

If the zone controller is controlling a circulator directly i'm not sure if the end switch will also start the circulator.

HomerJSmith

@Crispy, you should start your own thread as you will get more help for your needs.

hot_rod

With a mod con on zoned systems, ideally the boiler turn down would be close to the smallest zone. The small mod cons under 100K turn down to about 8,000 btu/hr. Any idea what the btu/hr of the smallest zone is?

There are a few high volume mod cons available the Viessmann 300or HTP has some tank style, 50 or 80 gallon condensing units that work great on zoned systems.

The mod cons handle multi or micro zoned systems much better that fixed output boilers, but excessive cycling shortens their life cycle

Crispy

Thank you. I was trying to be good and use the Search 😞. Boiler is an IBC 20-120 mod-con. Does that mean I will avoid the short-cycling? The smallest room is a bathroom with a 48" x 9" Snug CI baseboard. The boiler is at 160F (trying to keep the temp low while also the return >/= 135F) and that chunk of baseboard is rated at 1800 btu/hr @160F.

Crispy

@mattmia2, I was thinking if I paralleled all three end switches to the Zone 2 t-stat terminal in the zone control, one or more would fire zone 2 and I would be good.

hot_rod

Depending on the boiler model, the controller has functions to help limit short cycling that zoning can present. In the installer menu find some of those parameters

Max. power available for space heating 3

Burner modulation ramp C

Space heat delay P

mattmia2

https://forum.heatinghelp.com/discussion/comment/1876644#Comment_1876644

other people know the zone control better than me, but i think it is the end switch connection in the zone control that generates the heat call to the boiler.

with a mod con, the lower you can keep the return temp the better efficiency you will get so you want to use the lowest swt that can cover the load. If you have big cast iron emitters you can potentially get that temp pretty low and get adequate heating. You probably will want to install the outdoor sensor and set an outdoor reset curve for the swt.

you do have to balance the low swt and the cycle length a bit, lots of very short cycles at a low temp will be less efficient than longer cycles at a higher temp because there are some losses involved in the boiler shutting down and then firing again.