CH programmer that responds to external temperature

[echase]

I need a central heating programmer that has an input that makes the on time auto setting depending on outside or inside temperature or both. Can one be bought for <£200? There are complex ones for industrial buildings and offices but too expensive for me.

I want to enter the time when the building is entered and left and let the programmer work out how early to turn on the heating. It takes about one hour to heat up by 4C so after days of non use in 0C weather that is a 5 hours heat up time. But at end of heating season 30 mins is enough.

Needs 2 channels to heat 2 zones. Uses the same boilers for both but pumps/valves turn on and off each zone. The second zone heats up faster so ideally would like that one to cut in later but also be auto settable.

Superficially these Danfoss weather compensators seem like they might do the trick but can’t understand the info they give there http://heating.danfoss.co.uk/Content/84A57DA7-9FE7-4F5C-9F39-72E93943A0C7_MNU17521086_SIT313.html Also looks expensive by the time all the right parts of the system are bought.

 

[Fluffster]

What boiler do you have as a weather compensation unit usually just a 2 wire connection to the board in the boiler.

Pete

 

[echase]

What boiler do you have as a weather compensation unit usually just a 2 wire connection to the board in the boiler.

Pete

It is two Keston 170s although about to be changed. How would that 2 wire connection work as I need an adjustable input based on degrees per hour of heat up time?

Apologies for delayed response, looks like my emails notifications of new posts are not working despite being set.

 

[echase]

Danfoss answered an email I sent for more data and it seems their system is too expensive for us. Siemens do the Synco™ 200 range which looks similar and a bit cheaper but is not specifically a weather compensator. Anyone met them? It does seem to be all things to all men which might mean it does not actually do the exact thing we want if it’s too general.

Some events in this public building operate on a weekly cycle but others are one offs. One issue is that we want the time setting to be easy so non-experts can enter the time of a new event. But the more complex settings need to be password protected or otherwise difficult for the non-expert to accidently change.

In our heating system there are just two 230VAC lines to turn on/off each zone, with the boilers also being activated from these lines like on a domestic system.

What exactly does a normal weather compensator on a boiler do? If it is just making the water hotter depending on the weather then it may not be what we need as it is on times we are trying to change. Unless we always make the boiler come on 5 hours early and wind down the water temperature with the compensator to ensure it only just reaches temperature at the time the building is entered, But seems a bit wasteful when weather is not that cold to heat the building for 6 hours for a 1 hour meeting, even if the first 5 hours are not up to temperature. As we are changing the boilers soon it may make sense to have new ones with inbuilt compensation.

 

[Onetap]

I want to enter the time when the building is entered and left and let the programmer work out how early to turn on the heating. It takes about one hour to heat up by 4C so after days of non use in 0C weather that is a 5 hours heat up time. But at end of heating season 30 mins is enough.

That function is known as Optimum Start/Stop. I'm not aware of it being available on any domestic controllers, but I'd welcome info from anyone more knowledgeable.

Correction; available on the Hoineywell CM907, according to this thread;
//www.diynot.com/forums/plumbing/a-little-help-understanding-optimum-start.378808/

 

[echase]

Thanks for that. It is what I want but the CM907 stat that is referred to there only predicts ahead 2 hours it seems and we need up to 5 hours. I have contacted Honeywell to see if there is another model they do without this limitation.

I assume these devices have a learning routine that adjusts future performance based on past warm up time, as there is no setting to tell the device how quickly one’s building heats up.

I have some correspondence with Danfoss and their weather compensating programmer can do what I want but it needs to be connected to 2 of their 3 port valves that the programmer controls to adjust the right water temperature. That would add too much cost to our system. It seems more aimed at optimising the water temperature based on outside temperature than on adjusting the heat up time.

 

[matt1e]

I doubt that you are going to get any domestic controller to suit your needs, as they are designed to run domestic heating systems not commercial ones that I suspect yours is.
sorry to be the bearer of bad news

Matt

 

[Galoka]

Heatmiser also have optimum start in some of their models, both domestic and commercial. Though whether any of these will do quite want you want, esp. the domestic ones is another matter

http://www.heatmiser.com

On a related point, when the building is not used, does the heating just go off (with frost protection presumably). OK, not the same as your situation, but we have a fairly largish Victorian house, with a big thermal mass (all them solid uninsulated walls) which takes ages to heat up once it is cold. I found that a programmable stat that is set around 12-13 C at night stops the house getting so cold over night when it very cold outside and speeds the warm up time greatly. Without any great increase in the bills.

But then, our house of course is warmed up every day, a bit different with the sort of place you seem to be talking about if it maybe isn't used everyday

 

[echase]

Newton’s law of cooling states that the convection heat loss is proportional to the difference between ambient and inside temperature, ignoring draughts and radiation which follows similar but not exactly proportional rules.

So the longer it is heated the larger the loss in my view. So for a building heated once a week I see no value in heating it in-between, apart from for frost and fabric protection. As the building has existed for 900 years (this is a Saxon church) without any heating fitted it can tolerate no heating. Even for a daily heated building I doubt that it should be heated in between each occupation period. Although if the gap between each such period is low the amount lost is small and maybe does not show up when reading the bills.

One downside though with short heating periods is that the stone walls remain cold so there is a lot of convection induced draughts between the warmed air and the cold walls so the comfort levels are not great.

There is an oft quoted myth (my wife keeps mentioning it), particularly with hot water heating, that it is more economic to keep it running all the time rather than heat it up when needed because of all the energy taken to heat it up but I believe Newton puts paid to that idea.