Two boilers in multi zone setup

[cutleryman]

Apologies if already a topic but I can't find it if it is!

I have a largish (6500sqft+), old (1700ish), stonebuilt, badly insulated house with an existing central heating system which I think Mssrs Bodgett and Scarper did a DIY install on. It currently has a single oil fired 250,000btu (Firebird) boiler heating the whole system (initially from 42mm pipes then branching downwards in size as it spreads from the boiler).

I intend to fit zone valves onto each of the rooms to allow a central control system (HomeSeer - which controls other aspects of the home automation) to switch different rooms on depending on their use, eg in morning - just heat two bedrooms and their bathrooms and the kitchen; weekday evenings heat the main lounge, kitchens, and later the bedrooms and bathrooms; weekends heat the entire house. Firstly any problems with doing this (time isn't really an issue nor fitting costs as I'll do it myself)?

Secondly, I am tempted to install a second oil boiler but much lower power say 75,000btu(ish), then with some programing in HomeSeer, I could tell which boiler to fire eg in the morning when the radiator load is only say 60,000btu we use the small boiler and the large boiler when we need more. My logic on this is that it must be more efficient (given the price of oil) to run the small boiler at say 80% of output rather than the larger one at say 25% of its output as I presume that the Firebird will only be on or off in its output. Any comments???

Finally any body used the Grundfos Magna pumps in anything vaguely similar?

Thanks in advance. Cut

 

[doitall]

IF you are serious about long term savings and efficiency then you should consider;

2 x smaller condensing boilers approximately 35kw each piped into an low loss header, and from the header zone each area seperately.

The only problem in an existing property would be the extent of work required in re-piping the zones, but with weather compensation and the right controls savings in excess of 50% could be realistic, when compared to the existing boiler.

 

[Agile]

The only problem in an existing property would be the extent of work required in re-piping the zones, but with weather compensation and the right controls savings in excess of 50% could be realistic, when compared to the existing boiler.

Because domestic oil boilers dont modulate their power output then weather compensation will be limited to on/off modulation of the boiler which whilst still saving will not be as advantageous as on a gas boiler.

You may also find that you have to make up a weather compensation unit yourself.

Spending most of the money on insulation would probably be more cost effective particularly now that insulation is available in so many useful forms.

Tony

 

[doitall]

You're not thinking outside the box again Tony.

Most of the major controls Companies, Invensys, Landis etc all make Optimisers/compensators to operate rotary shoe valves.

 

[Deleted member 105431]

have you considered switching to LPG?

 

[doitall]

have you considered switching to LPG?

Why would he want to do that, when LPG is dearer than oil

 

[Deleted member 105431]

have you considered switching to LPG?

Why would he want to do that, when LPG is dearer than oil

because it is cleaner, easier to control, more flexible to site gas storage and boiler, lower maintenance, more efficent etc etc

 

[doitall]

have you considered switching to LPG?

Why would he want to do that, when LPG is dearer than oil

because it is cleaner, easier to control, more flexible to site gas storage and boiler, lower maintenance, more efficent etc etc

Oil tank and boiler are already sited so no problem.

Oil burners are just as clean as gas if serviced regularly.

Lower maintenance, agreed if you don't include reliability.

Oil boilers are as efficient and in some case more so than gas, etc, etc,etc.

 

[Deleted member 105431]

have you considered switching to LPG?

Why would he want to do that, when LPG is dearer than oil

because it is cleaner, easier to control, more flexible to site gas storage and boiler, lower maintenance, more efficent etc etc

Oil tank and boiler are already sited so no problem.

Oil burners are just as clean as gas if serviced regularly.

Lower maintenance, agreed if you don't include reliability.

Oil boilers are as efficient and in some case more so than gas, etc, etc,etc.

i'm not arguing just thougt it might be another option that's all. Another good point of lpg is that boiler can easily be converted to Ng if later added to the network.

 

[Agile]

Most of the major controls Companies, Invensys, Landis etc all make Optimisers/compensators to operate rotary shoe valves.

Yes, but they lower the temperature of the flow to the rads without lowering the flow temperature from the boiler. Its therefore not achieving all the benefits of full weather compensation.

This OP could probably easily knock up a simple comparator circuit and use a servo motor to just rotate the boiler temperature control as a VERY crude ( but effective ) form of weather compensation.

Tony

 

[doitall]

Optimisers, compensators with outside detectors etc have all the advantages of modern gas boilers, including, zone and temperature control with night set back, and they have been around longer than I have.

 

[Norcon]

Some controllers allow the boiler set point to be set between 6 to 16 k above the calculated mixed flow setpoint.
So if the controller decided the mixing valve must provide 30c to the heating circuit then the boiler set point can be set using the adjustable differential feature .

 

[doitall]

Some controllers allow the boiler set point to be set between 6 to 16 k above the calculated mixed flow setpoint.
So if the controller decided the mixing valve must provide 30c to the heating circuit then the boiler set point can be set using the adjustable differential feature .

Very good, the jobs yours

Anywhere near Clwyd

 

[ChrisR]

YOu could avoid all the zone plumbing with Honeywell's radio-linked programmable thermostatic radiator valve heads. I forget the name of the system but it sounds like what you want.

Each head has timing and temperature settings, and it sends a signal to the boiler if it's demanding heat.


yer tiz:
http://content.honeywell.com/uk/homes/Catalogue/Wireless Zoning System/3.1 CM Zone.pdf

 

[cutleryman]

Thanks for all the help guys. Plan is to stick with the oil for now although if we ever get NG here we may change (particularly as oil more than doubled in price in less than six months earlier in the year - wait to see what next load price is with oil now approx $100 barrel). Hadn't considered the idea of two boilers heating one tank before so will do some more research first.

As to zoning. had a look at the Honeywell system but more expensive than putting in zone valves under the floors (I'm replumbing the whole lot anyway so what's a few extra metres of pipe and a few zone valves between friends!)

Finally, I only found this site a few days ago and it is invaluable - thanks everyone again!

Cheers Cut