Running a central heating system

[Racerbear02]

We have a oil fired heating system which was installed 2 years ago, it has proved to be very economic in heating what is a large house ( 2 floors of 200sqm )and uses around 2200 litres per year which includes all our hot water for the year.

When it was installed, the default day and night temperatures as set by the installers were 23 degrees day and 19 night, we dropped this to 20 in the day and 15 at night as we are quite comfortable at these temperatures.

Following a service visit, the plumber has just said that if we had our range as 20 day and 17 night we would use less oil as the system would not have to work as hard as often when the temperatures were achieved in the house. This is a very well insulated house I might add.

Does anyone have any advice on this based on either real experience or research based theory?

I am just not sure what to think on this.

Thanks in advance

[Alcazar]

Do you think he is basing this on the cost of RAISING the temperature from night to day?

I seem to have read somewhere, differing theories on heating.

Theory one is that switching it off, then back on again, uses more energy than leaving it "ticking over", (does your plumber perhaps think that 15 degrees at night is like "off"?).

The second theory says the opposite.

I can't really coment on either, except to say that my father is a great proponent of theory one, and that I have suffered under theory two, working in an almost unheated building for a day or so, while a healting system that had been switched off over the Christmas break, struggled to get it back up to temperature.

Alcazar

[Babnik]

You could try both for a length of time and see how much you use. Not sure if you can accurately measure it though! I'd say go for what is comfortable, I can't think there'd be much difference!

[Mikew]

We use a programmable thermostat which gives us the temperatures we want, at the times we want. It can be programmed to at least 6 changes a day, same at weekends. The water temperature at the boiler is set to 60 degrees.

We have had only one season here, so I cannot comment on how much oil used, BUT this is similar to the same setup I used with gas in UK and it certainly saved us money there. (Modern house here, 140M2)

Mike

[IAN_S]

We find that unless it is very cold or that we are sitting about rather than working outside, that 18c/day 16c/night suits us well, anything less at night means it probably won't fire up and then works hard in the morning to get up to 18c when we need it first thing.

Given that thermostats will be in different places in different houses I don't think the actual figures mean much, it's just what feels comfortable to you.

[Ron Avery]

Your plumber is right, there are optimum max and min settings.  The theory about using more energy to go from stone cold to hot is correct, if you have a min temperature at night say 17C  it takes less energy to maintain this (as it is gradual reduction from the day temperature and then to goes back to your nominal daytime temperature)  than to boot up from a low temperature to a high daytime setting .  In the summer the C/H bit is off so this only applies in the winter periods.

 Also if your system is newish,  does it have  control options for dealing with cold snap in a warm period and vice versa?  These can help economy, This is adjusted by changing the parallelling and ratio settings to reduce or increase the rate of heat rise required to reach your settings.  I do not understand this but maybe Bob or someone  who really knows about such things can explain it.  My instruction book has all EU languages except English.

[Racerbear02]

Thanks for the assorted replies.

What I cannot decide is whether having the system trying to maintain a constant 17 will infact use more fuel than it having to go up from 15 three times a day, we have found that during the worst of winter, the house temperature will drop to 15, but that most of the time the temperature is above that so the system is not working. The lower setting is in effect for most of the day and night, it only goes to the 20 temperature for a couple of hours in the morning, an hour at lunch time and them 5 hours in the evening.

I understand that if we were coming from stone cold each time it would use more fuel, but cannot decide if maintaing the slightly higher temperature will be more cost effective, which is why I asked if anyone had definate experience or if anyone had done a study on it.

[Alcazar]

Anyone else's experiences, or a study done anywhere but at your property, could only be of limited use.

The only real way to check is to "suck it and see", but even that is open to distractions like a cold/warm spell when not expected.

Personally, I'd go with whatever makes you happy and comfortable. How much are you likely to save anyway?

As a younger man I always bypassed some filling stations trying to save a few centimes per litre. As fuel prices rose, I realised that often I was putting my journey at risk (of running dry), in order to save the cost of around half a litre of fuel. A bit daft, no?

Alcazar

[sue-J]

[quote]We have a oil fired heating system which was installed 2 years ago, it has proved to be very economic in heating what is a large house ( 2 floors of 200sqm )and uses around 2200 litres per year which ...[/quote]

I'm a building control system designer, working on heating and ventilation systems for large buildings. The lowering of heating temperatures during night-time (as opposed to turning heating systems off at night) is called 'night-setback' and is an established method of energy conservation in well insulated modern buildings. Essentially, with modern draught-proofed dwellings, good levels of insulation, modern controls, plus energy-efficient boilers, night-setback will use less energy to bring a dwelling back up to daytime set points than turning the heating off - thus saving energy. But it's never a simple as that...

If your system is a typical domestic system using thermostats (switches activated by heat or a lack of it) to control the boiler flow temperature and on/off time and thus the room temperature (as opposed to electronic temperature sensors) then thermal lag and switch hysteresis make accurate temperature control difficult. Bimetal thermostats often have a hysteresis of up to 6F, making accurate control difficult - although modern devices are more typically in the 2F range. This may not matter too much in the room, but can make a large difference back at the boiler, where flow temperature matter.

The most energy efficent control option for domestic dwellings is often an 'optimiser' - or weather compensator - a computerised box which measures outside air temperature, internal room temperature and boiler flow temperature then modulates the boiler flow temp to provide the desired occupancy temperature at the desired occupancy time . The system also 'learns' how long it takes to get the house up to occupancy set-point at any outside temperature and modulates the boiler flow temperature to minimise the amount of fuel burnt, to give the desired occupancy temperature. This comparision is called 'slope' and the slope of the compensator can be user adjusted to give a more or less rapid rise in temperatire to desired day-time levels.

But knowledge of such systems is usually low in domestic heating system providers, and the extra expense of installation means that these systems are rarely fitted, as few householders are convinced of their worth. Add in the perceived complexity of such devices and few householders bother. Yet, such systems often provide payback of their costs within about five years in the UK, from increased energy savings. They also often give better comfort levels, fewer wildly variating temperatures for example.

In the case of a simple domestic heating system with a single room thermostat and no boiler flow temperate modulation ( the burner is either on or off - controlled by the boiler thermostat) then night-setback systems tend to consist of a single thermostat for day use - and sometimes a secondary night- stat to control night time temperatures. In this case there is little the owner can do to control or optimise energy costs, other than reduce the boiler flow temperature in the summer and increase it in the winter, and keep the room stats down to the lowest level which gives comfortable room temperatures.

Further energy saving costs can be made by 'zoning' the upstairs radiators with Thermostatic Radiator Valves (TRV's) so the upstairs rads aren't producing heat unless called for, (heat goes up) and then if the budget allows, fitting TRV's to all rooms. Room or floor zoning in this way is very cost effective, and can be retro-fitted to most wet system for a comparitively small outlay. TRV's also compensate for the often 'hit

& miss water balancing to radiators carried out by heating installers. You're unlikely to have a properly balanced system, regardless of how much you paid to have installed, if your installer didn't provide you

[Lizzie15]

Phew! Thanks for that brilliantly comprehensive reply! My system has an outside sensor which I thought was quite cute- maybe it'll be useful! I haven't a clue as the system was put in in the spring and hasn't been used yet- are these outside sensors worth having then?

 

[Opel Fruit<P><BR>Opel Fruit, Dept. 53<P>]

French heating systems are still largely in the Iron Age. I suspect your outside sensor could be a Frost stat. If you have a Buderus or De Dietrich system or similar, you may well have the outside weather compensator. These have been around for several years, but are rarely correctly setup. Because no-one understands them. It's a pity, because they are worthwhile, and well ahead of the UK systems.

French boilers, oil particularly, are invariably non-modulating. Even the Buderus ones.

The top-end systems we fit (if requested) have sensors in every room (thermistors), and 2 port zone valves to isolate each rad or local rad group. The system also collects temperature from outside, the flow and return of the boiler and has a sun sensor. The control unit takes a day to wire and a day to fully program. It can control every aspect of the house (usually a large one) temperature at any time.

But it isn't cost effective for most domestic situations. TRVs are (well the good ones are anyway). Just be careful when positioning any room stats where there is a TRV locally.

[KathyC]

A completely untechnical reply. Does everybody keep central heating on at night? What about sleeping with the window open for fresh air? I thought heating costs were expensive in France? Thank God I'm moving to France for a simple life!

[Opel Fruit<P><BR>Opel Fruit, Dept. 53<P>]

No, most turn it off. The French are just about discovering timers too.

You need to keep the windows open at all times to provide relief from damp, saltpetre and mildew. 

[Ian 56]

My oil-fired central heating system is one which runs constantly with a temperature drop at night. It is 30 years old and the thermostat is an Ondal ‘Constant’ Type CT and no longer made. I would like to replace this with one which has more options. I have the wiring diagram, which shows three terminals used in the unit,

1. Phase coming in direct
2. Neutral coming in via one pump terminal
3. A return to the other pump terminal

 

For an easy life I would like to use a new unit, which had a similar wiring pattern but so far have not been able to locate one. I would appreciate any suggestions or advice. Opel Fruit sound the man!

 

ian

[Mikew]

Is not the phase wire for accelerator purposes? A modern battery operated programmable thermostat will not need this and switch the pump as needed via its own relay contacts.

Mike

[Opel Fruit<P><BR>Opel Fruit, Dept. 53<P>]

I have found these to be excellent, inexpensive and very flexible. This will do everything you want, with minimal fitting issues.

http://www.danfoss-randall.co.uk/Site/downloads/6890.PDF

[Ian 56]

Mike and O.F.

Thanks very much for your advice.

ian