Tie Zones together to prevent short cycle times

CTHeating

I am having an issue with short cycling due to small zones of baseboard heat. When the thermostat calls for heat, the boiler with cycle multiple times as it hits the high and low aquastat limits. I would like to tie two of the zones together, so when either thermostat calls for heat, both circulators will run. Can I just install jumpers across the thermostat connections at the relays? Please see image below. Thank you

SuperJ

Are those your only two zones? Are you using some sort of zone relay box to control the pumps and send the heating call to the boiler?

You've suggested an OR situation, you can also wire the thermostats in series to create a AND situation.

A more complicated version would be to AND the call the call for heat to the boiler (IE. only run the boiler when both zones call), but allow the pumps to run independently to distribute residual heat to wherever it is needed the most.

CTHeating

There are a total of 5 zones. I am using a zone relay box that controls the pumps and sends the heating call to the boiler.
I prefer the "or" setup to prevent a zone from getting too cold.
I like your more complicated version but will try the "or" setup for now.
Will my idea work with the jumpers as outlined in the image above? Just don't want to burn anything out.
thank you super j!

SuperJ

It will work as long as both thermostats are connected to the same transformer. I think your case the zone relay box probably has a transformer that powers the R wire to all the stats.

You wouldn't want to do it on two furnaces for example because they each provide their own 24VAC from separate transformers.

Another thought is to just combine the zones under one stat if one stat provides a reasonable control.

CTHeating

The relay box does have a central transformer. I'll have to try the jumpers and see how it works. Easy enough to try multiple ways.
thanks again.

NY_Rob

You just need to jump the t-stat switched lead at the relays, the other lead is common- no need to jumper that lead.

CTHeating

NY Rob,

Just to clarify. At the relays I have a "T" (white) and "TV" (red) connection, do I just need to jump the red wire?
thank you,
Joe

SuperJ

Hmm, you need to jump the W signals from the stats together whatever wire that is. (probably the white).
Do you have a multimeter? You could use it to confirm which is the common power wire and which is the call for heat.

CTHeating

got it. I do have a multimeter, I'll do what you suggested.

GBart

I would not do this, you are going to end up with uncontrollable temperature patterns and over and under heating.

The question is............why is it short cycling?? Is it a low mass boiler?? Perhaps down firing a tad and better controls like outdoor reset coupled with a something like Beckett heat manager/Intellidyne would be a better course of action. If there is sufficient heat in the boiler with low temp drop there is no valid reason to run the burner, that is what these controls do, they watch the water temperature drop and if there is low load the burner stays off.

Knowing what equipment we're talking about and the sq ft of the home would help.

http://www.intellidyne.green/index.php/products/heating/hw

CTHeating

The boiler is a 100K BTU Slant Fin cast iron, natural gas, non-condensing boiler (85% efficient). I’m located in CT and heating 2800 sq-ft. 2,000 sq-feet is heated with baseboard radiators, and 800 sq ft with radiant heat (concrete slab). There are a total of 5 zones, 4 heating and 1 for the indirect water heater. Home is older but has R38+ in the attics, R13+ in the walls, new windows, etc.
Each zone will run independently and kick on the burner if the aquastat calls for heat. The aquastat is a standard Honeywell with only one setting (currently at 180 degrees). All the zones have a separate circulator pump, powered from the thermostat relay box.

Zone 1: Kitchen 300 sq-ft (baseboard hot water)
Zone 2: Downstairs 750 sq ft (baseboard hot water)
Zone 3: Upstairs 750 sq ft (baseboard hot water)
Zone 4: Downstairs 800 sq ft (low temp radiant, fed from a mixing valve) new constructions, very well insulated.
Zone 5: 50 gal indirect water heater

I was looking at the Tekmar 256 boiler control. Would this help?

https://www.supplyhouse.com/Tekmar-256-Boiler-Control-One-Stage-Boiler-4150000-p
-Joe

SuperJ

@Gbart is right, if you reduce the water temp: the heating calls will last longer, you'll gain some efficiency (probably not getting 85% at 180f), and you'll have less space temperature fluctuations (more comfort).
The 256 is a pretty basic but functional control that will greatly enhance your boiler with an outdoor reset control. I think you should go to the 260 because you have DHW as well. Otherwise you'll have to cobble together some controls to run you boiler at a higher temp during DHW generation. You might be able to use the existing aquastat to control the boiler to higher temp during DHW calls.

The higher end 260 has a nice feature that can use an indoor sensor to fine tune the outdoor air reset setpoint. It can also completely manage your DHW control.

CTHeating

I'll have to order the 256 or 260. In the mean time, do you recommend reducing the temp? If so, to what? 170?

SuperJ

170f would be worth trying as a starting point, during mild weather you can likely go much lower, but space comfort isn't the only variable to watch. Make sure you can still generate adequate DHW, and your boiler isn't running at condensing entering water temperatures. (RWT less than 130-140f).

What is the boiler return water temp at the start, middle (after 5-10minutes of running), and end of a typical heating call?

Too low of return water temperature can be harmful to the boiler.

CTHeating

I am a bit confused by the aquastat adjustment. It’s a straight dial with an arrow but there is also some type of stop. Do I adjust the wheel and the stop? Picture below.

Gordy

Question is how many zones call singularly, and how many call at about the same time?

Selecting which zones to tie together plays into the above questions. You want to tie zones with same load characteristics.

100k in a 4 zoned system 2800 sf home is going to short cycle because the load is so small. Lowering the supply temp will help only so much.

STEVEusaPA

You’d be better off with a buffer tank. Lowering temperatures will only make the cycling of the boiler worse.

Gordy

^Yes when you think about it. If you cycle off of 180. 170, or lower just shortens the period of time before high limit is reached.

It lengthens the call for heat more, but does nothing for cycling during that call.

Eastman

Tekmar has much better controls that provide zone sync, but the cost goes up. The 256 or 260 used as an outdoor reset control will only exacerbate the problem. The optional indoor feedback mentioned will cause under heat in the zones without indoor feedback. A multi zone system requires indoor feedback in each zone. This is accomplished using a higher end model.