Another question:
After being recommended to us a S plan system with 2 port valves, I'm thinking why 2 valves and why not one 3 port valve?
What happens if you were to use 1 2 port valve?
Christmas Greetings to all.
Because 2 port valves are simpler and more reliable than one 3-port, probably.
You don't get separate control of heating and hot water.
Owain
An S-Plan system has 2 or more 2-port valves - one for each heating or HW zone, and provides independent control over the zones - only running the boiler and pump when one or more zone is demanding heat.
If you only have one 2-port valve, you cannot control your CH and HW separately - so you might as well have no valves at all!
A 3-port valve is used by Y-Plan systems - and also enables you to have CH or HW, or both together. It's main disadvantage is that the valve actuator plays a more strategic role in the overall control of the system than other plans, and is more complex than a 2-port actuator, and prone to failure, causing the whole system to stop working. It also limits you to 2 zones so you can't, for example, have separate upstairs and downstairs heating zones in addition to hot water. With S-Plan+ systems you can have as many zones as you like.
See
Agreed, the microswitches regularly fail.
Untrue, I had 3 zones with 3 port valves with a (modified) Y plan system (the supplier was out of 2 port valves when the system was installed).
You could with Y plan, but it gets complicated and unreliable.
I've converted to S plan. It has been much more reliable since. With Y plan I had to change microswitches at least annually. I don't think I've had a failure in the 5 years or so with S plan.
Which seems kind of odd, because the motor units are similar and there would be as many operations as before.
However, I agree with you. A system that I installed many years ago was fitted with two port valves because that seemed to be a better design decision. No failures. On the one that had been installed in the current house as original, there was a three way valve. These would fail about every 3 years or so and not always at the obvious times of the start of the heating season.
When I renewed the system, I switched to using 2 port Honeywell valves. I also fitted 28mm versions for the main ones to reduce flow restriction and 22mm ones in smaller zones. No problems at all with these in 5 years, although the boiler does have an automatic valve exercising function.
The main thing is that I want to be able to have HW only or CH only or both at the same time if a S plan system can do this then thats what is right for me
You can do that, although often controllers work in a hot water priority mode.
In old systems which used "gravity" for heating the HW cylinder, convection was used in the primary circuit to it to transfer the heat from boiler to cylinder. This ran pretty much continuously with the boiler thermostat effectively controlling the temperature. The central heating was controlled by a thermostat effectively operating the pump. This gave simultaneous hot water and central heating, but the cylinder would take quite a time to reheat because the transfer rate is poor. However, at least the house didn't get too cold while it was doing it.
With 3 port valve systems, the hot water takes priority. This means that if there is a demand from the cylinder, then the valve opens in that direction, and the boiler and pump run. This gives much faster reheating but even then because the coil in most cylinders is of limited surface area, it can still take quite a time to reheat and now the boiler output is directed away from the CH. Of course that will be worse if the cylinder is large and the transfer rate poor. In bad scenarios, the boiler will even cycle.
However, you can use a fast recovery cylinder. These have a coil of much larger surface area than traditional ones by having more turns or multiple small tubes and can take all or most of quite a large boiler's output. Reheat on these can be very short indeed and thus the boiler is returned to CH operation much sooner, and thus there is little drop in room temperature and probably nothing noticable if the system is designed well.
Another factor is that the boiler will run more efficiently in this way. During HW operation, the return temperature from the cylinder coil will be quite low and a lot of heat will be transferred. The boiler will thus modulate up to full power or close to it and condensing models will be well down the curve into efficient operation. When the boiler is returned to CH only operation, it will modulate down and run at lower power and temperature, again putting it into an efficient part of its working curve.
Certainly you can arrange the controls such that there are separate timed periods for CH and HW. That simply means that one or the other or both *can* operate. However, running the system such that both CH and HW demands are met simultaneously may well not achieve a desirable result of fastest results and best efficiency.
Why are the letters Y and S used, what do they stand for?
They are two of the so-called Sundial plans
A strange answer to this particular point! Some plans - notably W-Plan - do indeed give priority to HW, but as far as I am aware, all zones - space heating or hot water - in S-Plan systems have *equal* priority,
Not necessarily. It is true for W-Plan systems, which use a 3-port diverter valve - but Y-Plan systems use a 3-port mid-position valve which simply sits at its mid position when there are simultaneous HW and CH demands.
That depends on the implementation.
If you have separate thermostats and timeswitches perhaps. However, it is possible for thermostats and time control to be combined or even that the valves are controlled by or integral to the boiler anyway. Under these circumstances, the HW can be given priority.
Which is not a very good idea in a modern setup where lots of heat can be transferred rapidly to the cylinder.
OK, but in that case you will have departed considerably from the standard S-Plan definition.
Yes, an interesting one! My impression is that diverter valves were invented before mid-point valves, and that W-Plan has largely been superceded by Y-Plan once mid-point valves were in common supply. Maybe with fast recovery cylinders W-Plan systems are coming back - I don't know?!
I have a Y-Plan system with a programmable stat on the CH and usually [1] succeed in arranging the timing so that CH and HW are not both on at the same time.
[1] With optimum start on the CH stat, it may sometimes come on before the HW is fully hot - but it seems to cope ok!
I've always c The main operating requirements of Sundial Plans are:
1.The controls should provide full independent temperature control of both living space and stored domestic hotwater.It doesn't say anything about whether or not one can circuit can pre-empt the other. The timers and thermostats are essentially the same and it has been the valves that have limited what's possible.
IOW
W plan is the most restrictive because it permits flow in only one direction at a time.
Y plan less restrictive, but mid position valves do restrict flow.
S plan fully flexible in terms of what the valves can do.
That can all be avoided by using separate valves and controlling them with HW priority.
But the S-Plan as defined in
That applies to *all* plans - even the C-Plan
*And* it's possible to invent lots of additional variants which don't match *any* of the published plans - such as modifying the logic to change the priority.
Interesting that, seems a UK thing, I wonder it discourages heating engineers from being more inventive when designing a system for a particular property, but I suppose there won't be many situations where some variant of an S+ won't be suitable.
When I moved into this house in the mid 70's there was an S plan system with two Honeywell 2 port valves installed well it *would have been an S plan except the mechanical Randall 102 timeclock had only DHW ONLY - OFF - DHW+CH settings so you couldn't have CH with no DHW even though the cylinder stat would put it in that condition. I made my own control box with two three way switches for DHW and CH marked TIMED - OFF - CONT and a third on/off switch that bypasses the cylinder stat marked BOOST neon lamps indicate when each circuit is ON or calling for heat. Still going to this day.
They don't exclude anything in their specifications.
Exactly. The functionality is not limited by the specs. It is the valves that limit the functionality.
Of course. That's why Y plan was added when mid position valves became available, and S plan has developed with newer technologies such as Smartfit.
But by the same logic you could argue that a car is the same as a motorbike because it has an engine which causes the driving wheel(s) to rotate. The fact that you've added extra wheels and seats and a steering wheel and roof is insignificant.
I don't see what you're getting at. The functionality of an S-Plan system is achieved by means of a combination of the valves, timers and stats. You could, if you wished, achieve a different fuctionality with the self-same valves, simply by changing the external control logic. It's just that it would no longer be an S-Plan system.
If the spec. was for a means of transport using wheels then both would qualify.
Not all cars have to be basic Ladas. They can have air conditioning as well
Evidently.
According to Honeywell's specs. the requirements are listed above.
What if the c "The Sundial 'S' Plan is designed to provide independent temperature control of both heating and hot water circuits in fully pumped heating installations. Time control may be provided by a time switch or programmer."
It says nothing about whether or not one can be given priority over the other.
Good summary.
Its a bit like a combi, is Y plan. Simple and cheap if it suits in a small limited installation, but a PITA if its goes wrong or you need more flexibility.
Y plan can do it as well. Its more a reliability issue than anything else IMHO.
At least when one of my zone valves stuck 'ON' I just pulled the wires out and had the other CH zones and the hot water working..if a Y plan valve goes.,.you are screwed totally.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.