Zone temparature control question

[Roger2]

I would like to modify my existing Honeywell “S” plan 2 zone (CH + HW) system to a 4 zone system. House is medium/large 4 bedroom detached and the total heating load 30kW.

The “zones” will be

1) Hot water
2) Ground Floor Heating
3) 1st Floor Heating
4) Bathroom Heating-Towel Warmer.

The modifications I need to do to the existing pipe work for the zoning are fortunately relatively simple.
Temperature control will be
1) Cylinder stat. and timer.
2) Programmable thermostat in the hall with TRV’s in rooms.
3) Programmable thermostat in “study” with TRV’s in bedrooms and landing.
4) At this time no idea. Which is my question.

The bathroom is heated by a single radiator/towel warmer affair.

I assume A TRV alone will have no boiler interlock so is out of the question.
Due to the nature of a bathroom (rapid temperature changes - baths/showers) I’m again assuming a room stat would not give satisfactory temperature control and also that domestic room stats are not designed for use in a damp environment so would either not work properly or fail prematurely.

Can anyone suggest a solution or should I give up the idea of an independent zone for the bathroom as wishful thinking and just include it in the 1st floor circuit.

Thanks in advance for any suggestions.

 

[Agile]

I rather agree with what you are saying.

I am sure that there are some fluid phial thermostats with the sensor several feet away from the switch that would suit your application. Chris R will probably be able to suggest something to suit.

I really dont think that your house has a heat demand of 30 kW even if you leave all the wondows open.

The heat loss is pretty obvious but its the power input needed to maintain the house at 21 C. Thats usually about 14 kW for a 4-bed detached.

The radiator heat output is the total of the rad outputs and is most likely to be about 14 kW if they are sized to meet the heat loss.

The only think thats likely to be 30 kW is the boiler. That should be set to provide a heating output to match the loss, i.e. about 14 kW

Tony

 

[simond]

We use Honeywell CM67RF in this application. Being RF, there is no shock risk, the transmitter being battery powered.

Haven't had any failures yet due to condensation.

 

[croydoncorgi]

Is really worth making a zone with a single room (the bathroom) in it?
Practically, it might be sufficient to connect the HTR to the main boiler primary, independent of any zone valves, and put a TRV (with / without a remote capillary sensor, as required) on the HTR inlet. That way, the HTR will try to heat whenever there's a call from ANY of the other zones. Probably sufficient control for the room and MUCH cheaper than alternatives.

 

[ChrisR]

I'd go with CC's method.
An option is to put an electric heater into the towel rail so you can boost it if required. Still works on the CH water, they go up inside one of the sides of a ladder-style TR.