Energy savers reports

[tryitandsee]

Have just filled out a simple form on British Gas's web site to get a Energy Savers Report for my home address. Quite impressed, although basic, it asks the question why anyone has to pay £70 - £100 to get one from the 'surveyors'.

It has come up with a saving suggestion of installing a Delay Start timer that measures the temperature of the house thereby offsetting lenght of time on, depending on that temperature.

My question then, are they hard to wire up to the existing , in my case, Potterton programmer, as this looks like a good thing to have.

 

[D_Hailsham]

It has come up with a saving suggestion of installing a Delay Start timer that measures the temperature of the house thereby offsetting length of time on, depending on that temperature.

My question then, are they hard to wire up to the existing , in my case, Potterton programmer, as this looks like a good thing to have.

It will replace your thermostat and your Potterton timer for central heating, although you will need to retain your Potterton timer for Hot Water (assuming you do not have a combi boiler.

The best ones to buy are the Honeywell; CM901/907 are wired CM921/927 are wireless.

I've had one for two years and it not only turns the boiler on at the right time, so the house is up to temp when you get up, but it also controls the temperature to within about 0.5°C.

Wiring is very easy but it will depend on your boiler/system and which programmable stat you buy.

 

[tryitandsee]

Thanks DH

Will look further into it and see if my programmer will work with it.
Have found one for £37 - £40 (Honeywell 901 24 hour programable thermostat.)

 

[Agile]

A delayed start is useful but only if your boiler in non condensing or does not support weather compensation which is much better.

Tony

 

[JohnD]

does weather compensation have to be in the boiler? Can't it be added with external controls?

 

[Agile]

does weather compensation have to be in the boiler? Can't it be added with external controls?

Not in many cases without interfering with the circuitry as the flow temperature has to be varied and most boilers dont have that facility.

I would use a linear opto isolator.

Tony

 

[D_Hailsham]

Have found one for £37 - £40 (Honeywell 901 24 hour programable thermostat.)

Unless you work seven days a week, the 907 is probably the better choice as you can then set different times for the week-end when you have a lie in after a night on the tiles. They don't cost all that much more.

A delayed start is useful but only if your boiler in non condensing or does not support weather compensation which is much better.

But a condensing boiler does not know when you want to get up. It will just start at the time you set on the clock, which may be too early some days and too late on others.

Similarly for weather compensation; all that tells the boiler is the outside temperature. It does not tell the boiler how long it will take for the house to reach 20C by 0700.

Honeywell make the Chronotherm Modulation, model T8851M1000, which is OpenTherm compliant and incorporates weather compensation and optimum start. The only problem is that it is not available in the UK and all info on the web is in Dutch.

 

[Agile]

But a condensing boiler does not know when you want to get up. It will just start at the time you set on the clock, which may be too early some days and too late on others.

Similarly for weather compensation; all that tells the boiler is the outside temperature. It does not tell the boiler how long it will take for the house to reach 20C by 0700.

Thats not very relevant when there is weather comp.

If you give say 20 minutes to warm the house up then with weather comp it will make the boiler work flat out if its cold outside or will modulate back and run gently and in condensing mode if its not very cold outside.

Tony

 

[D_Hailsham]

If you give say 20 minutes to warm the house up then with weather comp it will make the boiler work flat out if its cold outside or will modulate back and run gently and in condensing mode if its not very cold outside.

Take the Vaillant VRC430 as an example. This has weather compensation which, according to the manual:
"Weather-compensated" means: At low outside temperatures the VRC 430 provides more heating output, and at higher outside temperatures lower heating output.

The programmer can provide up to three time periods a day. But these are the times at which the programmer issues instructions to the boiler. So, if you set the programmer to 20°C at 0700, the boiler will light up at 0700 and start raising the temperature. Whether the boiler runs flat out or gently will depend on the outside temperature, as measured by the outside sensor. But how long it takes for the house to reach 20°C will depend on the insulation of the house and how low the internal temperature has dropped overnight. You can adjust the heat curve, but even this does not tell the boiler how long it will take to get up to temperature.

The VRC430 has a parameter, "Max advanced heating time", which can be set to anything between 0 and 300 minutes before the "first time window". But the installation manual fails to say the purpose of this parameter. Maybe a crude form of optimization.

I still think that the only way to get the boiler to change the time it lights up is with an optimizing programmer, which can learn how long it takes to reach the required temperature and varies the start time according to the drop in internal temperature.

 

[tryitandsee]

I still think that the only way to get the boiler to change the time it lights up is with an optimizing programmer, which can learn how long it takes to reach the required temperature and varies the start time according to the drop in internal temperature.

I agree with that, but I assume this would need a thermometer outside and inside with a electronic learning 'chip' and a timer to measure the differing heat up periods. A small computer in effect. Would this not be expensive and therefore mitigate any cost savings in gas. Unless the room thermostat you have mentioned earlier does this.

 

[D_Hailsham]

I still think that the only way to get the boiler to change the time it lights up is with an optimizing programmer,

I agree with that, but I assume this would need a thermometer outside and inside with a electronic learning 'chip' and a timer to measure the differing heat up periods. A small computer in effect. Would this not be expensive and therefore mitigate any cost savings in gas. Unless the room thermostat you have mentioned earlier does this.

Yes the CM900 series does do this.

It does not need an external thermometer as the important factor is the rate of heat loss from the inside of the building, which depends on the insulation and is proportional to the difference in internal and external temperatures. The technology required has been known for many years (Honeywell had patents in the 1970's) and can now be incorporated into a silicon chip. The internal temperature is measured by a thermistor, which has the advantage of virtually instantaneous response to temperature change. When first installed, the device will start the boiler a pre-set time before that set on the clock (when you want the house to be up to temp). This may or may not be correct, so the internal computer adjusts the time next day and so on over the next few days, until it gets it right. More sophisticated versions - not available in the UK - also adjust the boiler temperature in accordance with the outside temperature.

The CM900 series are not that expensive; the wired models cost about £55 and the wireless about £75.

 

[tryitandsee]

DH Thanks for that.

 

[D_Hailsham]

DH Thanks for that.

Which boiler do you have? There may be something specific to that boiler available.

 

[tryitandsee]

Potterton prima f 50 which is a sealed system for central heating only, not hot water. With a Potterton EP4001 electronic programmer, no room stat but rads have TVRs.

Weird set up I know, but I converted the old place back from three self contained flats.

 

[BigBurner]

It appears there is confusion between an optimiser (delayed start) and a weather compensator.

Optimisation is different to delayed start. Optimisation will delay the boiler's start to reach the start occupation time temperature setpoint and "increase" it too. The better versions will optimise the off period too (it works out when to turn off the boiler to keep the room setpoint constant right up to the off time). If the building is at setpoint, even at the start of occupation time, some will still keep the heat off. The simpler versions will always bring on the heat at the start of occupation time.

Delay start is just that, it only delays the start and always brings in the heat at start of the occupation time.

Weather compensation is varying the flow or return temperature depending on the outside temperature. The lower the outside temperature the higher the flow or return temperature (some sense the flow temperature, others the return). The flow or return temperature can be trimmed up or down with room temperature influence to maintain a room temperature setpoint.

If the weather compensation and delayed start are separate units, there should be no problems, condensing boiler or not.

When the two are integrated, the room temperature sensor can be used by the weather compensator to trim up or down to suit. The delayed start can use the compensators outside temperature sensor. If OpenTherm compatible, then instead of switching out the burner (on-off control) the burner modulates giving more precise control and better efficiency when using a condensing boiler.

Only a few boilers have OpenTherm compatibility, if you can get one I advise to get it. Keston are OpenTherm, Atmos and few others. I believe German Vailant's UK models are not. OpenTherm really do make a difference in control and you are not stuck with a expensive dedicated makers kit (like Vaillant, Glow Worm, etc) as OpenTherm means anyones controls will work on your boiler.

The sooner the UK makers adopt OpenTherm across the board the better the control system will be on UK system. The cheaper it will be too, as third party makers will compete supplying the controls. A simple OpenTherm room thermostat will modulate the boilers burner to maintain the room temperature. That means a condensing boiler may be modulating to give only 35C flow temperature, giving exceptionally high condensing efficiency. But only if the boiler can modulate down to a very low kW rate.