NEST: hot water and heating query

nowackis

Hi guys,
I have NEST thermostat, which controls hot water or radiators. I wonder if it is possible to "set it up" in following way:
- when I turn heating on, it will automatically heat up water (at the same time)
- when I turn "hot water" on, it will only heat up hot water

From what I see I have 2 two-way motor valves connected to "grey box" with multiple cables. They control heating and hot water.

During NEST installation I was told its not possible, but "common logic" tell me it should be doable. Hope someone with experience can advise.

Thanks a lot!

Steve

So - do you you have a motorised valve for radiators and another motorised valve for hot water?

If true then it's no problem with a nest controller.

nowackis

Yes, I have motorised valve for radiators and another motorised valve for hot water. Nest works fine as it turns on either hot water or heating.

What needs to be done to achieve following:
- when I turn heating on, it will automatically heat up water (at the same time)
- when I turn "hot water" on, it will only heat up hot water

Steve

nowackis wrote: »

- when I turn heating on, it will automatically heat up water (at the same time)

You can't, they are different. You set each one separately.

- when I turn "hot water" on, it will only heat up hot water

Just set the hot water schedule.

Maybe I am not understanding your problem correctly, can you explain in more detail?

nowackis

Let me describe it.
Basically in current combination when I turn the heating on, I heat up radiators only (not hot water tank).
When I turn the hot water on, I only heat up water in water tank (not radiators).

I though about energy saving during the winter time, so when I would turn the heating on, it would automatically heat up radiators and water tank (open both motorised valve). It would be "automatic process", without me programming NEST to do both at the same time or something.

In the summer time, when I would like to heat up water tank, only motorised valve for hot water would open.

I presume it would require "extra" cable patching or something, but I would appreciate if you can comment further.

Dardania

nowackis wrote: »

Let me describe it.
Basically in current combination when I turn the heating on, I heat up radiators only (not hot water tank).
When I turn the hot water on, I only heat up water in water tank (not radiators).

I though about energy saving during the winter time, so when I would turn the heating on, it would automatically heat up radiators and water tank (open both motorised valve). It would be "automatic process", without me programming NEST to do both at the same time or something.

In the summer time, when I would like to heat up water tank, only motorised valve for hot water would open.

I presume it would require "extra" cable patching or something, but I would appreciate if you can comment further.

I have to ask, why would you want to align these two? Is it to avoid running the boiler at different times - your basically trying to optimise the boiler run time & load it as high as possible?

nowackis

yes, I would like to avoid running the boiler at different times.

I live in apartment and I have water tank high for around 2m. the bottom part is designed for hot water (around 60cm), so its very small capacity. the upper part is designed for cold water (around 140cm). I often run out of hot water, so I though about optimizing usage during winter.

Wearb

nowackis wrote: »

yes, I would like to avoid running the boiler at different times.

I live in apartment and I have water tank high for around 2m. the bottom part is designed for hot water (around 60cm), so its very small capacity. the upper part is designed for cold water (around 140cm). I often run out of hot water, so I though about optimizing usage during winter.

It wouldn't be difficult to do what you need, but you might be better off asking this question on the electrical board. I can think of ways of doing it, but I would prefer that you got the advice from an electrician.

Dardania

nowackis wrote: »

yes, I would like to avoid running the boiler at different times.

I live in apartment and I have water tank high for around 2m. the bottom part is designed for hot water (around 60cm), so its very small capacity. the upper part is designed for cold water (around 140cm). I often run out of hot water, so I though about optimizing usage during winter.

okay, so I understand your motivation - it's a heat scavenging optimisation initiative...

As wearb notes later, there would be a way to do it, with relays et al., or a plumbing mod with non return valves - however to be honest, it may not be as effective as you think. Issues like heating the water, only for it to lose it's heat over time while standing in the cylinder might occur.

There are lower hanging fruits to optimisation you could look at here, such as insualtion levels on the tank (probably factory installed) and all of the pipework around it.

A slight bit more difficult (depends on if your boiler supports it) - you could run different boiler output temperature setpoints depending upon if the boiler supports that e.g. 60C if heating water, less if heating radiators - that way you can get some condensing efficiency. Possibly the Nest offers this function through opentherm capability.

Do you have TRVs on your radiators? can optimise run times there by knocking off boiler sooner rather than overheating spaces (like bedrooms)

Steve

nowackis wrote: »

Let me describe it.
Basically in current combination when I turn the heating on, I heat up radiators only (not hot water tank).
When I turn the hot water on, I only heat up water in water tank (not radiators).

I though about energy saving during the winter time, so when I would turn the heating on, it would automatically heat up radiators and water tank (open both motorised valve). It would be "automatic process", without me programming NEST to do both at the same time or something.

In the summer time, when I would like to heat up water tank, only motorised valve for hot water would open.

I presume it would require "extra" cable patching or something, but I would appreciate if you can comment further.

You should stick to a timer then.

With nest, you program when you want hot water as a timer. For house heating, you tell it what temperature you want at a given time or day. It then decides when to run the boiler.

I can see your point and it is a good one but nest will not do that for you. I have 2 zone timer with a house stat and water stat and program it as you have said.

ed112

Hi Nowackis,
What did you do in the end here?
I have the same concern - the boiler running independently for the heating and for the water.
I would have thought it more efficient to heat the water while the boiler was already on for the heating?
Thanks..