by ericmark »
Fri Jan 24, 2020 12:07 pm
The heating system is made up of boiler, programmer, valves, thermostats, pumps, and tanks.
The valves if fitted come as two or three port, the three port means Y or W plan and 2 port S or C plan. The Y and W are very similar don't often see a W plan, Y can heat CH and DHW at same time, W gives DHW priority. The Y plan uses both N/O and N/C contacts on the tank thermostat.
With a S Plan normally two motorised valves one for DHW and one for CH and always the hot water tank will have a thermostat.
The C plan has three versions, they all use thermo syphon (gravity) for DHW only the CH is pumped, the change is how the DHW is controlled or not controlled.
Early C plan DHW could not be turned off, no real problem in winter, but hard to use in summer as only control was time boiler runs for, no allowance made for how much DHW is used.
The first improvement was to add a thermostat to the hot water tank. As with Y plan both N/O and N/C contacts on the tank thermostat are used, and the thermostat means the system can be left on DHW all summer and boiler only fires up when required, and the tank can be kept cooler. It made no difference in winter, only in summer was there an advantage.
Last improvement was adding a motorised valve to the DHW, this allows the DHW temperature to be reduced in the winter, and you could even turn it off, however many boilers relied on being cooled after being turned off by transferring heat to DHW, both the Y Plan and first two C plans allow this (Default on three port valve is DHW and some thermo syphon will pass through a pump even when turned off) but the last C plan and the S plan does not allow boiler to cool into DHW so it needs a run on fan to send excess heat out of flue when the boiler turns off.
C plan is used a lot with oil, and old gas boilers, Y plan was popular before the economy drive, there seems to be a move to the S plan which is easy to add zones with so you can heat upper and lower floors independently, seems to me an odd method, as we all tend to use our homes different, so I for example use two upper floor rooms as bedrooms and one as an office and one as a craft room, and entrance level dinning room only used in the evening, and after 8 pm kitchen hardly used, pop in to make coffee, so I really want each room independently controlled, just 2 zones does not really work, so I have wifi programmable TRV heads on entrance level except for kitchen, which like the 4 room upstairs has a blue tooth programmable TRV head. So I have 8 independent zones, (living room has two radiators so 9 programmable TRV heads).
I got the wifi heads with the whole idea of latter getting Nest, but by time I had got Nest, Nest had withdrawn support for the Energenie MiHome TRV heads, so in real terms the £45 (plus cost of hub) wifi head does very little more than the £15 eQ-3 bluetooth heads, and since the eQ-3 has the ability to manually control, you don't NEED a phone to swap Eco to Comfort and they have a window open function.
Also I have found Nest mounted closer to centre of house and higher than the TRV often shows 2°C higher than the TRV, so the follow command does not really work, I set the TRV in the hall 2°C lower than Nest also in the hall.
So today Nest is the odd one out, Hive, EvoHome, and Tado all have dedicated TRV heads, Nest does not, Hive is also an odd one out, that does not work with OpenTherm rest do, but your boiler not opentherm anyway.
I have used a TRV and a wall thermostat in the hall in two houses, this one and mothers, in mothers house the TRV and wall thermostat was closer and once set worked well, this house two doors between then and a stair case next to hall radiator means a big delay between radiator getting hot and the heat reaching the wall thermostat, so even with Nest it tends to over shoot, so Nest is set to rise 0.5°C per hour in the morning to reduce the over shoot, the TRV's in the rooms ensure the rooms at target temperature but hall heats up over 4 hours. This is the advantage of Nest I can set it to raise 0.5°C per hour.
