Few questions on my current modern gas multizone central heating

stamjoe

I've a new house and it has a 3 zone system, 2 floors and a stat per floor and hot water. But there's also an outside thermostat facing North on the side of the house.

If I have either floor zone set to come on, the rads just get slightly warm if it's not freezing out, I was told that the outside stat is influencing to the house economically how hot to blast the rads, all my floor stats are set to 20c. So usually I just have the floor zones on just for 10mins each but it doesn't really do much but the builder told me you can just turn on the hot water zone too at the same time as whatever zone is active and then then rads are hot as expected regardless of outside temperature.

Anyone got some more information on this?

I've now set the hot water schedule to happen at the same as the upstairs and downstairs zones were scheduled to come on, prior to this I had the hot water zone on a different time schedule. I presume this is less economical timing the hot ground floor or first floor zone to coincide.

John.G

10 minutes each will achieve little or nothing, suggest a hour each at least, if the rooms are up to temperature then the room stat will cut out the boiler anyhow.
You should also have a chart showing you the outside temperature compensation curves for the boiler temperature. Assume you have a condensing boiler? oil or gas so running the heating separately (without HW) may/should be more economical if the HW raises the boiler SP temp to enable the HW cylinder reach 60C.

stamjoe

Yeah you're right condensing gas boiler, so really I should not be setting the hot water zone to coincide with the other floor zones to get that blast of heat? When the Hot Water zone is on at the same time it really is a lovely bit of heat and you feel it instantly. Big difference in getting the house upto the stat temperature when the HW zone is on, otherwise it really doesn't get near the stat temp.

John.G

Something a bit strange there, can you see what the boiler (water) temp is both with the HW only on and the rads only on, it should be displayed on the boiler front and that will tell a lot. I wasn't aware that the boiler SP temp will change automatically depending on whether HW or CH mode is selected, anyhow do have a look at those temps and post back.

Rads are designed to give their rated output at 50C difference between the mean rad temperature and the required room temp, so if you require a room temp of 20C then the boiler temp would need to be ~ 75C (with a return temp of 65C) to give the rated radiator output of 50C, ie ((75+65)/2 - 20)), however if you just assume that for whatever reason that your boiler temp is 60C and the return is 50C then you will have a "35 deg" rad ((60+50)/2 - 20)) which will give you 63% of the rated output but this should still heat up your rooms even though it might take a lot longer, except that your rads are fairly badly undersized/underated in the first place, IMO all rads for use with condensing boilers (the only boilers available now) should be rated by a factor of at least 1.5 because of the above.

Edit
Found a bit of info there re a standard compensating curve for a Viesmanns, where 0C=65C 5c=58c, 10c=52c, so with our present mild temperatures your boiler may be running at ~ 55c, so you may have "25 deg" rads with output reduced to 41% so as gary71 suggests below ask your installer if he can modify this curve.

Have your installer look at reducing the impact the outdoor sensor is having on your heating flow temperature.

The only difference between heating and hot water demand usually is the boiler ignores the outdoor sensor when the hot water is calling for heat.

John.G

gary71 wrote: »

Have your installer look at reducing the impact the outdoor sensor is having on your heating flow temperature.

The only difference between heating and hot water demand usually is the boiler ignores the outdoor sensor when the hot water is calling for heat.

That makes sense, have you any typical outdoor temperature compensating curves? for interest.

John.G

John.G wrote: »

That makes sense, have you any typical outdoor temperature compensating curves? for interest.

Nope, far to complicated for me

on my boilers it’s a matter of just pressing + or - to alter the impact of the outdoor sensor, they keep it simple so fellas like me (lazy) can do it.

John.G

Just saw your post so maybe stamjoe can do, or get done, similar, interesting one way or the other.

Have you any idea what your (compensated) SP is just now? and if available, your return temperature.

stamjoe

Yep that's what I'm saying I was told by a few installers that by turning on the HW zone it ignores the outdoor stat, so it heats up the house much quicker so I guess by turning that zone to coincide with my heating it defeats the purpose of the economical reasons of having that outdoor stat.

The rads will be twice as hot if you turn on the HW zone i.e. ignoring that outdoor sensor, just seems to no clarity on should you run the system as intended with the outdoor sensor reducing the temperature inside.

John.G

Can you post your gas boiler make/model and, if available, its compensating curve.

stamjoe

stamjoe wrote: »

Yep that's what I'm saying I was told by a few installers that by turning on the HW zone it ignores the outdoor stat, so it heats up the house much quicker so I guess by turning that zone to coincide with my heating it defeats the purpose of the economical reasons of having that outdoor stat.

The rads will be twice as hot if you turn on the HW zone i.e. ignoring that outdoor sensor, just seems to no clarity on should you run the system as intended with the outdoor sensor reducing the temperature inside.

You have a system design that doesn’t meet your needs, it requires adjusting of the outdoor sensor sensitivity or it’s removal.

If you find at this time you can achieve your required need by running the heating and hot water together then I would do that to you find a better solution as your not wasting money unless your home is getting to hot reaching unsuitable temperatures.

stamjoe

I've an ideal logic system 15, it only gives the status of the burner on the front, I suppose if you have an outdoor sensor the system is supposed to run for longer right, rather than shorter 1 hour bursts of heat.

John.G

The attachment shows how the weather compensation works, if its not working properly ie faulty sensor or whatever, then you can get very low CH water temperatures, you didn,t give the exact model description but on some of these boilers you can influence CH water temp by simply turning a knob on the boiler front, when HW only is requested then the boiler water temperature is set to 70C.
If it were my boiler I would get someone to check it out as IMO one years savings would probably pay for the visit.

stamjoe

Interesting read on the compensation thanks for that! I did have multiple people initially check it and they said each time just turn on the HW if you want it to heat fast .

I just double checked on the front it says ideal Independent System 15 not logic as I stated earlier.

stamjoe

I had a guy out yesterday and he said to just remove the compensation sensor, same as the last 2, no one seems to know how it's actually meant to work in real world scenarios. There is no adjustment everything is automatic.

John.G

stamjoe wrote: »

I had a guy out yesterday and he said to just remove the compensation sensor, same as the last 2, no one seems to know how it's actually meant to work in real world scenarios. There is no adjustment everything is automatic.

If the boiler flow temperature is displayed on the boiler front then you can just read it off with CH only on and CH+HW on and that will tell you what the setting is for the present ambient temperature, or did I ask this previously??

Yes, you said that it is not displayed.

stamjoe

Unfortunately everything is automatic on this unit