S plan heating controls

[Dave]

Can anyone see anything wrong with this? - a zone valve each for zones 1-3 and one for the DHW, - z-valves 1 & 2 (upstairs/downstairs) controlled by timer/thermostats, - z-valve 3 (airing, workshop, towel rails) controlled by a timer plus a workshop frost stat in parallel with the timer, - DHW z-valve controlled by timer and tank stat (timer also controls DHW circulation pump), - all the (N/C) z-valve contacts are wired in parallel and used to switch L to pump and boiler.

... this all seems pretty simple, have I missed anything?

I've seen references to "advanced" control systems which claim to be more efficient, presumably by modelling thermal inertia and learning from heat demand patterns - has anyone any experience of them?

[Greg C]

Seems a bit like overkill. Over the years I've been equally idealistic only to conclude simplest is best. Realistically you must ask yourself if you are designing in features that in the long term use you don't really need. A few conservative alterations can save you days of work time and a lot in materials. Zones 1 & 2 are a very good idea ( I have them) but ONLY if you have an enclosed staircase with a self-closing door. Otherwise it's a waste of time. More important is independent thermo valves to all radiators (*except the bathroom) which would exclude the need for zone3 IMHO. You can set a thermo valve for frost protection.

Motorised valves do go wrong and should be seen as a potential weak point in the system. Fit them in an easily accessible position and anticipate 5 years as the lifetime of the motor (which can be replaced with the valve in situ). Also keep the controls, or a manual override, in your kitchen or as near as possible to your living area because you'll save on bills by switching off as and when necessary.

As the weather improves the most expensive way to heat water is to leave your CH boiler cycling at the mercy of a cylinder-stat. Wiring the system to exclude "HW only" may not be the most convenient but can save a fortune. Unless you need an unusual amount of HW then it's cheaper to boost your immersion heater and shut down the boiler over the summer.

Greg C

[Set Square]

Sounds reasonable to me. A few minor queries/comments:

What's the DHW circ pump for, and when does it need to run?

Do you really want the workshop and towel rails in the same zone? You could even consider having the towel rails unzoned (i.e. straight off the flow pipe after the pump but before the zone valves) so that they get hot whenever *anything* is on.

I would use a conventional 2-channel programmer plus 3 programmable room stats. It's easy to turn everything off at the programmer then. Use the timer in the programmer for DHW, and set CH to 'constant'. Use the timers in the programmable stats to determine when each zone *actually* comes on. Most programmable stats have a built-in frost stat function so if they're in the right place, you don't need a separate frost stat. Some - like the Honeywell CM67 - have an 'Optimum Start' version which decides when to turn on the heating - depending on prevailing conditions - once you have specified the time by which the house/zone must be up to temperature.

[Alan]

In message , Greg C wrote

Surely it is cheaper to use the source of energy that is the cheapest?

I have my boiler timed to come on prior to the need for the hot water (or occasionally on a manual override). This also has the advantage of using the pump every day so I don't get that 'seized pump syndrome' on the first cold day of Autumn.

[John]

He gave up in the end but I used to have a customer who swore he could save £15 over the course of a summer by switching his old and inefficient boiler off and using his immersion heater. However he didn't factor in the autumn call out when his wall mounted boiler fuel pipe drained down and it wouldn't pick up the fuel. so with an average £50 call his saving was actually -£35 His wife realised before he did and the fall out was spectacular!

[Greg C]

If that were so we'd all be using solar panels. A gas boiler isn't terribly efficient as most of the heat disappears up the flue especially during ignition and "warm up". During summer months cheaper "Economy 7" lecky-power heats our extra-large cylinder which generally lasts all day.

Never experienced that but I'd guess it could also be avoided by briefly running the pump every couple of weeks.

Greg

[Dave]

It's a fairly long run from the cylinder to the furthest tap so I'm arranging a hot water loop. The pump circulates DHW round the loop, controlled by the DHW timer and a pipestat.

I agonised over this but if the house thinks it's up to temperature, and there's no DHW demand, I still want to be able to heat the towel rails and airing cupboard. The boiler and cylinder will be in the workshop so having a rad (with TRV set low and a frost stat) will protect the machinery and the boiler/cylinder/pipes.

That's probably a sensible idea as I need a timer anyway for the DHW. Our room stat/timer only has 2 temperature settings, are there any which allow several temperature set points?

[Christian McArdle]

Actually, modern condensing boilers are more than 90% efficient.

Christian.

[Dave Plowman (News)]

Only if you have a very inefficient boiler, or heating loop, or are using cheap rate electricity. But I alter my main clock to just run the boiler long enough in the morning to top up the water, and again in the early evening.

Years ago, I did actually measure the amount of gas required to heat a full tank from cold, and compared it to the same thing using the immersion. Then, it was about half the cost. With not the most efficient boiler in the world, but a pumped fast recovery cylinder.

[Dave]

A further thought ... presumably it would be worth arranging DHW priority so that the heating zone valves shut if the DHW valve is on ... ?

[Christian McArdle]

Just don't put a balancing valve on the coil. It will steal most of the heat anyway, especially if mounted close to the boiler.

Christian.

[Set Square]

I don't quite understand that. Surely you want the pump to run at times when you're likely to *draw* water, rather than when it is being *heated*?

Not sure what you mean. Do you mean are able to control several things at different temperatures at the same time, or are able to control one thing at different temperatures at different times? programmable stats can do the second of these. For example, the CM67 can vary the temperature 6 times per

24 hour period.

[Dave]

Slightly reversed logic compared to mine... I was assuming that the water will be heated at times when we might want it and therefore the pump would run at the same times - however I can see that there's an advantage to a separate pump timer. (The pump is on the return side of the loop so doesn't affect flow when it's off)

... snipped

Currently we have a timer/stat (Ex-Maplins) that controls the whole house (un-zoned) but it has just 2 temperature set points, any hour interval can be set to either temperature - I was wondering if there was a stat/timer with a choice of more than 2 temp set points.

[Dave Plowman (News)]

Mine has four periods in any one day which you can set to what you want time wise and temperature wise. Ie nighttime, morning, daytime, evening. You can then designate days in the week as working or at home days, and have a different set of temps for those.

[Dave]

What make/type is it?

[Dave Plowman (News)]

[Set Square]

The usual idea with stored hot water is that you heat it ahead of when you want to use it, and keep it hot in an insulated cylinder. You've then got plenty when you need it.

My Honeywell CM67 programmable stat has 6 settings per day when on "Auto" - each of which can be set to anything you like. Mine is currently set to something like:

7:30 - 21 deg (on Optimum Start , so that it's up to 21 deg when I get up) 9:30 - 18 deg - (to give background heating when we're up and about) 12:30 - 21 deg - (to give a lunchtime boost while we're sitting down) 13:30 - 18 deg - (background heating again) 17:30 - 21 deg - (for sitting around in the evening) 23:30 - 12 deg - (heating off overnight unless it's exceptionally cold)

You can also have a completely different programme each day of the week if you wish.

In addition, there's an "Off" position - which isn't really off but acts as a frost stat, at 5 deg I think - but configurable.

Actually there are a few more bells and whistles - like a holiday setting - where you can tell your heating to use just the frost stat setting for x days (up to 99) and then come on to have a warm house when you return from holiday.

-- Cheers, Set Square ______ Please reply to newsgroup. Reply address is invalid.