Controlling new complex heating system

[leenowell]

Hi,

We are greatly extending our house and with it fitting a new heating/ hot water system. In summary it will consist of the following..

- 2 system boilers

- Megaflow tank

- One room (zone) with water UFH

- 3 zones (1 per floor) for the heating

- 1 "zone" to cover the towel rails in the bathrooms so that they can be warm in summer with the heating off

- secondary loop for the hot water to reduce draw down time of the hot water in the other side of the house

- all rads with TRVs

The question is how on earth do I control all this???

Having looked her and search the web a lot, I have seen the following "possible" solutions and was wondering if anyone here has a fairly cost effective solution?

Option 1 - programmable room stats The thought here was to have a programmable room stat per zone (assuming the UFH is an additional zone) located in the hallway/ landing of each floor and in the room with UFH. Centrally control the hot water and towel rails on a timer.

Seemed a good solution until my wife thought about the scenario where we come in during a time when the heating is off and want to turn it on again. We would have to go to each room stat and turn it on....

Option 2 - use some X10 controllers I have not had any experience with these but in theory I guess you could control them via a timer and also in the scenario of coming in when everything is off, switch them on with a central controller(s) from anywhere in the house. Has anyone used these? Is this a good idea?

Option 3 - a comercial controller. I saw that Honeywell seem to do a fancy controller which optimises the bolier firing and timing based on your temperature requirements and the outside temperature. I couldn't get a great deal of information (nor find anyone who sold it!!) but believe it is called an AQ2000. This would resolve the issue of managing the 2 boilers and the central control when you get into the house but then provides the flip side of how do you switch the heating on when you are upstairs?

In summary, despite a great deal of searching, I haven't been able to come up with anything that is flexible and resolves the problems above. Wouldn't it be great if you could call it to turn the heating on on your way home (like you can with alarms to switch them off)??

All ideas and thoughts appreciated. Also, any issues with the current design?

thanks in advance

Lee.

[David Hansen]

On Tue, 20 Jan 2009 03:29:32 -0800 (PST) someone who may be [e-mail] wrote this:-

North/south zones are generally better, unless whole floors will be unoccupied. With north/south zones weather compensation is easier as is coping with solar gain.

Master time clock. Programmable thermostats have occupancy programmed into them. Master time clock will enable or disable output from every thermostat. Going out, turn off heating at master time clock. Coming in, turn it on at master time clock, only those rooms where the thermostat is programmed for occupancy at the time will warm up.

[leenowell]

The logic behind the zones per floor is that the top floor will hardly ever be used and the middle floor is where the bedrooms are so won't ordinarily be used during the day.

As you say, the master clock is great for switching everything off or reducing everything (e.g. only have heating on for 1 hour a day when on holiday or something) but unfortunately, doesn't solve the "I now need the heating on" issue.

thanks

Lee.

[meow2222]

Even better is to separate the concepts of timer zones and temp zones, andhave one temperature zone per room. Its cheap to do with bimetal stats. Your timers each control several rooms, but local to each room, each room has its own stat. This means you can switch off or turn down the heat in any one room at will. You then have a master switch to turn the whole system down to frost protect, and use that when you go away. Note on frost protect setting the system relies on a single central stat, the individual room stats are effectively not operating in this mode since they will all always call for heat, but the system will be controlled then by the frost stat..

NT

[leenowell]

individual room stats sounds like an idea. Do you have a link to a bimetal stat as I haven't heard of these before. How would I get each floor to come on at different times?

[Doctor Drivel]

Firstly a simple system change. Get rid of the Megalow and fit a heat bank/thermal store. This does the DHW at mains pressure. All the zone can be taken off the store of water directly or a small header for the 3 rads zones and bathroom rail zone. Each zone has a pump and check valve in front. Simple and the same price as zone valves and less problematical. The rad and rail zones can have Smart pumps on each, which means TRVs all around and no silly by-pass valves or wall thermostats. The UFH can be taken directly off the thermal store cylidner lower down where temperaures are lower. Use a single speed pump and blending valve. The boilers? Take each one to the store cylidner with its own flow and return. No header. No need to sequence the boilers. Have two cylinder stats for anti-boiler cycling purposes - the boiler comes in the reheat the whole cylidner ASAP in one long efficvient burn.

That is the mechanical side sorted.

Control: Timer for DHW, which calls in the boilers. In summer one can be manually switched out. Each boiler requires its own isolating switch.

Cheap single stage Timer for each zone. It switches on a relay. The relay switches the Pump for the zone and the boilers. Relays are approx £5 from Maplin and put in a nice large plastic box. Have a wall stat for the UFH between the timer and the pump.

The timers can all be in one position in the house.

Each function (zone, boioer DHW) work totally independently. In winter have the DHW come well before the CH, so that the CH rads get hot immediately by dumping the hot water directly into heating loops from the cylidner store.

For an explanation:

will make the thermal store/heat bank for you. Specify the number of tappings, etc. Stainless steel. back if you wnat to know more.

[David Hansen]

On Tue, 20 Jan 2009 05:04:00 -0800 (PST) someone who may be [e-mail] wrote this:-

Depends on the settings, but seems to fit the "we come in during a time when the heating is off and want to turn it on again" condition which was specified.

In an individual room which one is using at an "unusual" time, just adjust the temperature on the thermostat temporarily. When finished set it back or leave it until the next time period, when it should go back to timed operation.

[meow2222]

Cheap thermostats are bimetal, as are almost all old stats. The idea is to keep the inital costs down and thus improve payback. Bimetals work more or less as well as electronic, and are far more reliable.

could implement your originally suggested zoning, so each floor is on its own time control, the only difference is you have one thermostat per room instead of one stat per floor zone. This means the room stats must control the rads in that room via a valve of some type. Electricaly controlled TRV heads are available for under =A330, such as the Danfoss RA 2912.

There are choices as to how you control boiler firing, depending on the details of the setup.

Maybe it would be better to talk of floor sized 'zones' and room sized 'subzones' to reduce confusion.

NT

PS this gives more info on the Danfoss products

[John Rumm]

(Ignoring the boiler sequencing for a mo, and just looking at the room and water temperature control)

If you went with this as a baseline, but added a separate programmer in an accessible location that fed all the prog stats then you should be able to achieve what you want. Program all the stats to achieve the required temperatures that you need. Set them such that you maintain a reasonable minimum fallback temperature when you think the zones will be unoccupied and/or overnight. Set your timed programmer so as to achieve the minimum level of running that you require when out or on holiday etc using its "once" or "twice" setting. For normal operation switch it to "always on" and let the prog stats do their stuff.

When you come in, you flick the programmer back to always on. The prog stats will then set about heating any zone that is currently below its target temperature for that time period.

Depends on how clever you want it to be - and how much effort you want to put into getting it all working. Do a google on this group for some of the information posted on this in the past.

Have a look at this thread on sorting out the demands to the boilers:

[leenowell]

John,

Thanks very much for your reply..... Sounds like a plan but I am a little confused about the following

In normal operation, wouldn't the programmer be set to "always on" anyway as we are relying on the programmable stats to decide when heating should be on by zone? If it wasn't for some reason, switching it to "always on" wouldn't override the times set on the stats would it. i.e. if the stat says turn off/ go to minimum temp at 10:00 and at

11:00 I switch the central programmer to "always on", the stat will override it?

thanks

Lee.

[Jon Fairbairn]

That's not electrically controlled; it's a remote bulb connected by a capillary. I've not seen a Danfoss thermoelectric head for anywhere near that cheap. The link Richard Skeen posted in the "Timer TRVs" thread for Heatmiser in-line wax valves was the cheapest I've seen, but I don't know what TRVs the heads would fit, and I don't know how easy it is to get the heads separately.

[John Rumm]

This is true.

I was assuming you would set the stats such that they keep the house at the temperature you require when you require it. However the addition of the programmer would would allow you to reduce the heating for times when you are not following your normal pattern of occupation - i.e. everyone out for the day, or on holls etc. You would then have the timer set to run the heating just enough to keep it ticking over. To be fair a frost prevention stat would probably do this just as well.

If you particularly wanted to be able to force the heating on at a time when the programmable stats are already satisfied, there is nothing stopping you adding an override switch or programmer. A simple one that has a "boost" facility would allow you to push one button and have the heating run for an hour regardless of the stats being satisfied. However I am not quite sure why you would want to do that unless you plan to program the stats to a very low temperature for the bulk of the day when you expect to be out, and need to account for unexpected periods of occupation.

[leenowell]

Hi John,

This is exactly what we wanted . However, I guess the programmable room stats would turn a motorised valve on as well as firing the boiler. In the case of hitting the boost button, the boiler may start but the valves not open. Not sure if this is the way it works though?

thanks

Lee.

[The Natural Philosopher]

With a many zones system, you wire all the contact for the motorized valves in parallel and take the resultant two wires back to theboiler. One goes to 'CH live'(may be timeswitched) and the other fires up the pump/boiler.

That allows the stats that drive the valve motors to be on a different live..useful as you may want to link into the local ring main for that.

[John Rumm]

You would connect your override button(s)/programmer across the contacts of the room stat(s). That way it will fire the system/zone in exactly the same way as the stat.

[Dave Liquorice]

Ooo, no, please. The entire heating system should really be fed via a single DP isolator switch. You don't want bits here and there live when other bits or not. Apart from the safety aspect when working on the system it's quite likely to confuse people if it acts strangely if a ring main trips.

As this system is likely to "evolve" I'd run all the contacts of any device back to a central wiring cabinet and do the appropiate cross connections there. I've done that here and it makes changing things very simple, like adding pump over run or possibly replacing the relays with a PLC.

[Andrew Gabriel]

Note that boilers aren't very good at driving tiny zones of a radiator or two. A modern condensing boiler just won't be able to modulate down to low enough power to drive so few radiators without ending up cycling off and on, and that could well counteract any gains you might expect by micro-zoning (and the hysteresis before switching back on can mean your one radiator has to cool quite a bit whilst you are still demanding heat). You really need a more intelligent system that would look for, say, the 3 zones which most need heating, to ensure there's some minimum load and that you drive the zones into synchronising their heating demands to some degree. One way around this is to use a heat store, but then you're increasing the complexity, cost, and maintenance, and it's unlikely you'll make any saving that comes close to compensating for this.

Another trick I've done is that when all demand for heat ceases and you tell the boiler to switch off, I switch the flow through a zone which hasn't been operating, so that I cool the boiler by dumping the heat into a cooler heating zone (where it stays inside the house), rather than having the boiler blow it out of the flue together with cooling the circulating water in the pipes.