Plan Y to Plan W

Malc · 16 Dec 2004

Hi,

Is it possible to do a plan W from a plan Y, without chnaging the valve of course. I'm trying to optimise my new oil boiler and I reckon it would be better on plan W where HW has priority. Of course I could just use the time clock but that's not as flexible.

CH4 · 16 Dec 2004

You would have to rewire from this:

To this:

ChrisR · 16 Dec 2004

Where did that come from CH4? It wouldn't work! HW wouldn't come on unless the CH was on, and....

Try Honeywell's suggestions:
http://content.honeywell.com/uk/homes/catalogu.htm#SECTION 3- SUNDIAL PLANS

You can make a suitable valve from a 4073 by connecting the white and grey wires together.

CH4 · 16 Dec 2004

ChrisR said:
... HW wouldn't come on unless the CH was on, and....

That is correct Chris. A "Priority" W-plan (in this case DHW) only needs one switched live (timed) contact to control the system. The W-Plan document, on the web-site that you provided link to, states (on page 2):

"Time Control - Any time switch or
mini-programmer may be used
provided that Heating cannot be
selected without Hot Water".

So, the CH only comes on when the cylinder stat is satisfied.

Malc · 16 Dec 2004

Thanks for that. But, I now see that I don't exactly mean a plan W, but rather a WY

. That is I can separately control HW and CH but if HW is on then it takes priority.

My reasoning is that a HW boost would be useful about 5pm but I don't really want the valve flicking back and forth as the room thermostat clicks on. Thermal lag in the house is long enough that it would be better to heat the water, then do swap back to the house when the water is hot.

Actually the other thing I could try is making the HW circuit much lower resistance which should have the same effect I guess. The HW circuit has a gate valve and currently I've set it about the same as the CH circuit so that on HW only it does not trip the bypass.

In general it seems to me that having HW and CH on at the same time is not that clever an idea, at least at startup. It takes about 30 minutes for my radiators to heat up. So during that time the same water going through the HW circuit would be taking heat out of the HWC.

oilman · 16 Dec 2004

In general it seems to me that having HW and CH on at the same time is not that clever an idea, at least at startup. It takes about 30 minutes for my radiators to heat up. So during that time the same water going through the HW circuit would be taking heat out of the HWC.

Not really. You might as well have water going to the radiators, as the surface area of the coil in the cylinder can't pass anywhere near the output of the boiler. All that will happen is the boiler will cycle on it's thermostat more. Just have a Y plan, it will save you having to put in an abnormal system.

Malc · 16 Dec 2004

I'm not sure about the HWC not being able to take the power (14kW BTW). The HWC is new and claims 20min reheat (screwfix). I've run HW only for 20min with a cool tank and the boiler ran continuously.

PEDANTICVINDICTIVEMAN · 17 Dec 2004

Just use a twin channel programmer and time the hot water to come on 30 mins earlier than the heating, make sure your cylinder stat is set correctly so it will switch off when the water is hot enough, now go away.

ChrisR · 17 Dec 2004

Well CH4 I ask again where the diagram came from. I think it's wrong, Honeywell think it's wrong, the customer thinks its wrong.....

Malc · 17 Dec 2004

Just use a twin channel programmer and time the hot water to come on 30 mins earlier than the heating, make sure your cylinder stat is set correctly so it will switch off when the water is hot enough,

now go away.

Which I said in my first post.

Of course I could just use the time clock but that's not as flexible.

Fair enough if you didn't read that and were trying to be helpful, not if you are just being rude.

oilman · 17 Dec 2004

PVM? rude?

CH4 · 17 Dec 2004

ChrisR said:
Well CH4 I ask again where the diagram came from. I think it's wrong, Honeywell think it's wrong, the customer thinks its wrong.....

It's based on a diagram from an old Honeywell book of Sundial heating plans:

In my sketch, I used the existing 'CH On' switch as the system timer, though it could just as easily have been the 'DHW On' switch.

It's purely academic now, but in what way is it wrong or wouldn't work?

CH4 · 17 Dec 2004

Malc,

The heat exchanger coil in your cylinder must be very effective to take 14 kW continuously for 20 minutes.

So, if you still want your system to have priority DHW, then a simple modification to your Y-Plan, which should work, would be to insert the 'Normally Open' contacts of a power relay (with a 220-240 V ac coil) between 'CH On' and the Room Thermostat - energising the coil from 'DHW Off':

The CH would, thus, only come on when the cylinder stat is satisfied or when the DHW is off at the programmer.

Malc · 17 Dec 2004

Thanks for the suggestion. Using a relay was the only way I could think of too.

The easiest seems to be use the time clock or keep with plan Y but either don't turn the HW on until the rads have warmed up some and/or open the HW restrictor fully so it takes most/all the flow.

I'm currently looking at what happens when I'm just heating the water since this will be what happens in summer. I can run for about 15 min at which time feed water is at 80C and boiler cuts out. 1 min later it restarts and then runs for 1min, and so on. I'm going to try using the time clock to give me 10min on / 10min off cycles and see if that works any better. The tentative theory being that 10min rest period will allow the cylinder to stabilize more.

According to HRM, (they think), the cycle time is best at least 3 min running, i.e. short cycle < 3min. Honeywell CM67 datasheet give a minimum run setting of 4min for oil so some agreement there.

PEDANTICVINDICTIVEMAN · 18 Dec 2004

Do you go train spotting by any chance in a green anorak with the hood full of dandruff and wear little round spectacles

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Plan Y to Plan W

Similar threads