condensing oil boiler upgrade

Don't fit anything you don't agree with it's not rocket science;), I'm not a flag waver for weather compensation or condensing boilers, its not my job or calling to convince anybody of anything, I have a opinion it's based on 25 years working in the industry and I'm qualified(well I have the papers anyway:cool:), I'm not trying to sell any idea or control system, the things i'v advised are things I'd happily do in my own house, if that's not accepted, fine, I don't mind:D

Iwannahurl

Iwannahurl wrote: »

but the alleged benefits seem to rely a little too much on human behaviour for my liking:

[

you can say that about any control system, most home owners don't know or care to know where their filling loop is or take responsibility for basic heating system controls.

heinbloed

heinbloed wrote: »

Gary71 is asked about the cost savings associated with the co-installation of condensing boilers with weather compensation units.



and answers



Reduced fuel costs are not the same as cost savings, Gary71.
Anyhow:

How much was saved with what meassures, due to which influences ?

How much of the (maybe achieved) fuel costs were due to fuel replacing (other, cheaper fuels used instead of gas - the open fire, stove, the OAP bonus for coal and gas etc.) how much was due to changed consumer behaviour, how much was due to changed weather pattern, how much was due to the new boiler, how much was due to better in-house controls, how much was due to the weather/changed heating degree days/passive solar gain? How much was due to the weather compensation?

How many recorded cases are there to draw data from?

Sorry, I feel bad now I didn't ask any of that, they were just so happy their bills went down I must have forgot

Plombier

Heating Systems.

A building heating system is designed to provide full heating on design day; in practice an additional margin is allowed to provide extra power during boost period of intermittent heating. The capacity of the heating is therefore greater than required for operation in all but the coldest conditions. For buildings heated by conventional a radiator system, operation during mild weather with the flow temperature at full design value, typically 80C, results in control problems high temperature swings and consequential discomfort; it also results in wasteful heat loss from hot water circuits and plant.

Two-position (on/off) control

In this mode, the controlled device gives either maximum or minimum output, typically on and off. To prevent a high frequency of switching, with attendant wear on plant and equipment, it is necessary for a switching differential between the switching on and the switching off of the controlled device. With the heating on, the space temperature rises until the sensor output exceeds the set point. The heating then switches off and stays off until the temperature falls through the differential and reaches the lower limit, whereupon it switches back on and the cycle repeats.

The room temperature continues to rise for a time after the heating system has been switched off, this is caused by the fact that the radiators still contain water at full design temperature.
The room temperature continues to fall for a time after the heating system has been switched on, this is caused by the fact that the radiators now contain water well below the temperature required.

Two position control results in a swing in temperatures about the set point and a mean temperature that that normally lies below the set point with the consequential discomfort and wastage as mentioned above.

Weather compensation.

Compensation control requires a continuously variable output of the controlled device. The controller produces an output that is proportional to the error signal; i.e. the difference between the value of the controlled variable and the set point. The control output increases from 0 to 100% as the input falls from the set point. Unlike on-off control there are no swings in temperatures about the set point but a steady state condition prevails, increasing comfort and minimising wasteful heat loss from hot water circuits and plant.

Compensation control allows the whole building to be controlled as one unit, or as a limited number of zones, thus eliminating the need to provide a large number of separate space controls. It has the added advantage of limiting heat loss in the event of increase load, e.g. if windows are left opened. A practical addition to compensation control is the addition of Zone Trim. The standard weather compensation circuit is used, with a zone trim applied to the compensated water flow temperature. The trim
modifies the set point by a margin proportional to the difference between the measured zone temperature and the desired set point.


Figures.

Energy usage based on degree hours and calculated Building Base Temperature.

Energy / K Casual Heating Overall Mean Base Hourly Days Energy
U kW/K^-1 Gains kW SP Efficiency Temperature Tempeaature Monthly kWh/hour
1.00 1.50 21.00 0.75 7.00 19.50 12.50 16.67
0.50 1.50 21.00 0.75 7.00 18.00 11.00 7.33




Shown above is the hourly energy demand at row 100% load and in row two 50% load.

The heat output from a radiator is proportional to the 1.3 power of the difference between the mean radiator and the room temperature (deltaT) it is not a matter of simply halving the flow temperature to get half the power, in this example the flow temperature for a 50% load is 48.0C.

DeltaT 82.5C flow 21C room drop across rad 11C = 55.0C (No condensing)
DeltaT 48.0C flow 21C room drop across rad 10C = 32.5C (Full condensing)


The column Building Base Temperature column and Energy usage colum shows the point.

oldsmokey

Oh Lordy, seems I've opened a little hornets nest here - thanks everyone for the input - theres a lot of opinion out there! I reckoned i was doing the right thing in going for a condensing boiler, but even that appears to be a moot point now...I guess its time tocall in someone who knows his heating onions and let him size up our set-up...but i know a little more now at least..

Iwannahurl

IMO none of these things can be taken for granted.

On the basis of what I have read here, I am certainly tempted to consider upgrading my boiler and controls. However, as always, I will carefully research all the details first.

Let us know how you get on! If possible, and if you go for the condensing option plus additional features like weather compensation, it would be good to have accurate before-and-after information on fuel consumption.

Plombier

As a simple explanation imagine two identical cars on a journey from Dublin to Cork.

Car one has its accelerator removed and an automatic on/off switch fitted in its place (in a heating system this is a thermostat), when you start the car the switch automatically goes to the on position and the car will accelerate at maximum acceleration until it reaches 100 kph (in a heating system the set point) and at this point it switches itself off until its speed drops below 75kph(in a heating system the set point less the switching differential) where it switches on again and continuously repeats the cycle all the way to Cork with the car engine going from full acceleration to no acceleration regardless of the effort required to propel the car, not going to be very economical.

Car two on the other hand has cruise control fitted and is set to maintain a steady speed of 75kph(in a heating system the set point), the cruise control continuously monitors the speed and adjusts the acceleration according to the effort required to propel the car forward (in a heating system this is weather compensation).
If the car travels uphill the cruise control increases acceleration (in a heating system this is cold weather).
If the car travels downhill the cruise control decreases acceleration (in a heating system this is mild weather).
There may be one or two miles on the journey where maximum output from car two is required (in a heating system these are design conditions).

Now if the cars speed can be kept below 80kph the engine efficiency can be increased by 10% - 15%(in a heating system this is condensing mode).

Car one will possibly drop below 80kph for a very short while when the switch goes from the off to on position, but will quickly accelerates beyond it again (in a heating system very little condensing).

Car two on the other hand will always keep the acceleration to a minimum thereby maintaining maximum efficiency at all times (in a heating system maximum condensing mode).

Iwannahurl

I'll have to have a closer look at that CIBSE literature for a start.

Certainly it has always bugged me that my central heating system keeps kicking in even when the room temperature is adequate given the outside temperature. It seems that the reading on the zone/room thermostat is not an absolute, whereas I expect 18 or 22 degrees to be just that, within reason! It also drives me mad that the thermostat often comes on when I turn it down!

I try to reduce short cycling, or whatever it's called, by keeping the boiler thermostat low. No need for boiling water in the taps especially, IMO.

oldsmokey

Thanks Plombier - the analogy makes sense - it also appears to me that its probably worth going the extra few quid on the condensing boiler (given the govt grant) , even if it wont be in condensing mode all the time..true?
Is there a heat-merchants or supplier who you could recommend in the North Cork / Cork city / East Kerry area? Someone without an 'axe to grind'?...pm me if you wish...With regard to installation, theres a local plumber who's living nearby, and we therefore are kind of obliged to use, I just dont know how 'tuned in' he is - could a reasonably competent man fit the thing or is it better to get a 'specialist'?..I know, lotsa questions, but its nice to get it right first time..thanks again.....

DGOBS

even when the boiler is not in condensing mode, it is still more efficient that a standard boiler as it has more surface area exposed to the flue gases (and hence less loss)

Iwannahurl

What about the costs of a new (replacement) boiler?

Roughly how much for unit and installation?

How long to recoup costs in fuel savings?

heinbloed

DGOBS writes:

even when the boiler is not in condensing mode, it is still more efficient that a standard boiler as it has more surface area exposed to the flue gases (and hence less loss)

As there any independant document anywhere available which says so ? Source? Link?

heinbloed

Iwannahurl wrote:

What about the costs of a new (replacement) boiler?
Roughly how much for unit and installation?

It depends what you want and where you buy it, as usual.

How long to recoup costs in fuel savings?

This depends on replacement costs, future fuel and maintenance costs, life time expection and previous costs of the old system.

stiophan

MOD NOTE

deleted. Poster replying to a very old thread.