Zone Control on LPHW Heating System

[budmurf]

This might be a failry broad question but I have a building with 3No. LPHW heating circuits serving radiators in north/centre/south zones.
Temperature control at the moment consists of 1No. thermostat controlling a common mixing valve.
I am proposing to provide individual temperature control for each zone/circuit in an effort to reduce the energy bill for the building. This would be done by seperate stats controlling individual mixing valve on each circuit and inverter control on the main boiler injection pump.
Does anyone know what effect this may potentially have on energy consumption/bills as in a percentage reduction etc.

 

[ChrisConley]

What does No. mean, you use it twice 3No. LPHW and 1No. thermostat... off the top of my head No would mean Normally Open.

For energy reduction I'd recommend variable speed pumping on your secondary loop and 2-position valves on the loops. Without fully understanding the system it be harder to get more in depth.

 

[budmurf]

Apologies, 'No.' just refers to 'number of'.

The system consists of 2 LPHW boilers feeding o low loss header arrangement via 1 boiler injection pump and diverting valve controlled which is controlled by an immersion stat in the return o the boiler.

The low loss header feeds 2 circuits. The first of these serves a heating circuit with time-clock control on the pump only.
The second circuit is actually a header system with 3 circuits controlled via a timeclock for each circuit and a common 3-port mixing valve controlled by a single room stat.

Hope this is somewht clear description of system without going into too much detail.

 

[ChasBean1]

A system diagram would be helpful. Philosophically I agree with ChrisConley. Can you do that? All else being equal, you should see some savings due to better compensation for sun, but the percentage could vary based on placement of sensors, glazing, building shape, etc.

 

[budmurf]

Chasbean1,

I'm attaching a hand sketch of the system which I did on site. Hope it comes out alright.

 

[ChasBean1]

Nice sketch! Interesting system, with a 3-way on the primary, a header (essentially a decoupler) and another 3-way on the secondary. This system however has out-thunk me, so whoever designed it might be on a higher realm.

I like simple. No problem with your idea of splitting zones. I do have a problem with more 3-ways and more complexities. See/digest attached suggestion and post back when you can.

Best, CB

 

[budmurf]

Thanks for the sketch.

I agree with your 'keep it simple' philosophy.
Are you suggesting omitting exisitng 3-port valve arrangements? I would be a bit reluctant too change too much a system which appears working fine at the moment.
I'm assuming the v1 lets the boiler injection pump act as a shunt.The VFD's could still work in conjunction with V2

 

[ChasBean1]

Yes, with this arrangement I'm not sure why the three ways would be necessary. Your sketch shows burners controlled by external temperature (meaning OA?) - that would be an open loop - no direct feedback mechanism... If you get rid of all the three-ways, let OA temperature determine your secondary loop set point, then use the secondary loop temperature to modulate boilers I think it would be much simpler and quite possibly more efficient.

Do you have a written sequence of operation for the system that you could also upload?