Radiator Booster - any thoughts?

Mayen

Cardew wrote: »

Really?

Would the siezed engine account for my son having difficulty pedalling?

Definatly, you forgot to attach the water based pre-heat system and no doubt the oil pre-heating too, I think its supposed to be over 60 degrees before turning over. Might make his seat a little hot for him though.

I'm not sure your version conforms to the current aerodynamic designs, does it pass invigilation and does it still have the old fuel expensive off-throttle blown diffuser or is just muscle induced torque through peddle rotation.

doughnutmachine

surely the way this technology works is by reducing the heat loss to the outside of the house? it seems obvious the air temperature between a wall and radiator will be high (say 50 degrees), if the outside air temperature is 5 degrees there will be a fair amount of heat loss through the wall.

with this booster the temp between the wall and radiator should be a lot lower. since heat loss is a function of the temperature difference the inside air temperature and outside air temp i can see this booster would make a difference if it is situated on radiators mounted on exterior walls.

zeupater

doughnutmachine wrote: »

surely the way this technology works is by reducing the heat loss to the outside of the house? it seems obvious the air temperature between a wall and radiator will be high (say 50 degrees), if the outside air temperature is 5 degrees there will be a fair amount of heat loss through the wall.

with this booster the temp between the wall and radiator should be a lot lower. since heat loss is a function of the temperature difference the inside air temperature and outside air temp i can see this booster would make a difference if it is situated on radiators mounted on exterior walls.

Hi

In theory, partially - but here's the reality ....

From what I've seen, the units which are available retail seem to have a single 12V/1.2W 50(ish)mm fan built into an extruded plastic body approximately 0.7m long.

Looking at the first source available for a ~50mm 12V DC fan rated at ~1.2W (http://www.maplin.co.uk/brushless-12vdc-axial-fans-1806)we can see that the 40mm unit is rated at 1.92W (12Vx160mA), which is 60% more powerful than the 1.2W radiator booster, but can only force 210l of airflow/minute, so let's be (very) generous and say that a 1.2W unit would be rated at 180l/minute, that's 10800 litres/hour (10.8 cubic metres) ....

.... follow so far, so let's look at the volume of air naturally convected by just a small radiator ....

A typical small single panel type11 800(ish)mm radiator is rated at around 900W at a 50C differential temperature to the ambient air, and due to the extended transfer area provided by the fins, let's say that 60% of the heat is provided from the rear of the radiator and that the average convecting air temperature is raised by 25C above ambient, therefore somewhere around 45C (((70-20)/2)+20),

.... follow so far ...

We now need to look at the specific heat capacity of air raised by 25C in order to calculate the approximate convection rate to provide 900W of cooling to the radiator ... for simplicity, let's just leave thermal expansion and relative humidity aside and work on 1cubic metre of air having a mass of 1.1kg at 45C (raised 25C), air to have a specific heat capacity of 1.005 kJ/kg per degree C temperature difference, so 27.6kJ/cubic metre of airflow (1.005x1.1x25), therefore multiplying by this 0.000278 gives us energy expressed in kWh .... that's 0.0077kWh/cubic metre of convective airflow.

.... Okay now for the final bit in the calculation ....

Taking into consideration that 60% of heat is being convected from the rear of the type11 (single panel finned) radiator airflow is obviously cooling the radiator by 0.54kW (0.9x0.6) .... which must be achieved by ~70cubic meters (0.54/0.0077) of airflow at the rear of the radiator per hour.

Looking at the above we can see that the natural convection from the radiator is forcing 70 cubic metres per hour into an obstacle which is able to cope with 10.8 cubic metres of forced air throughput per hour, therefore, rather than enhancing airflow the booster will restrict it, with natural convected air simply spilling out around the sides & edges of the booster because it physically can't cope. The booster, not being able to mechanically provide significantly more airflow than natural convection achieves little (/no) more than a passive deflector such as a radiator shelf ..... remember, this exercise is based on a small type11 radiator, so just think about the airflow through a type21 radiator, or even a type22 .... :whistle:

HTH
Z

doughnutmachine

zeupater wrote: »

Hi
Looking at the above we can see that the natural convection from the radiator is forcing 70 cubic metres per hour into an obstacle which is able to cope with 10.8 cubic metres of forced air throughput per hour, therefore, rather than enhancing airflow the booster will restrict it, with natural convected air simply spilling out around the sides & edges of the booster because it physically can't cope. The booster, not being able to mechanically provide significantly more airflow than natural convection achieves little (/no) more than a passive deflector such as a radiator shelf ..... remember, this exercise is based on a small type11 radiator, so just think about the airflow through a type21 radiator, or even a type22 .... :whistle:

HTH
Z

so perhaps if the unit was better designed it would work in certain situations. if a 1m2 radiator is located on a badly insulated wall of U value 1.5 and a fan reduced the temperature between the radiator and wall by 30 degrees it would save 45 watts of energy.... ok not a great amount, but the science behind the product "works" to a certain extent.

zeupater

doughnutmachine wrote: »

so perhaps if the unit was better designed it would work in certain situations. if a 1m2 radiator is located on a badly insulated wall of U value 1.5 and a fan reduced the temperature between the radiator and wall by 30 degrees it would save 45 watts of energy.... ok not a great amount, but the science behind the product "works" to a certain extent.

Hi

The calculations were based on a convective airflow raised to 45C, therefore a 25C increase above ambient ... how would you therefore reduce the temperature by 30C ??

Anyway .... assuming 45W of heatloss is correct and the reduction could be achieved by sufficiently increasing the airflow then you would need a really powerful fan unit, probably consuming well over 45W ..... remember that the breakeven point from a cost perspective would be based on the differential cost of gas fired heat vs electricity for forced airflow, therefore with a cost ratio of approx 3:1 you would be losing out if providing anywhere over 15W of forced airflow ....

My view is that the radiator booster is a poor solution to a problem ... drawing warmed air and placing the unit on the top of a 70C radiator will likely reduce the design-life of the mechanical components by a factor of 8 (20000Hrs to 2500Hrs), electronics somewhat less, as well as reducing natural convection. Any forced air unit would be better placed below the radiator in a position where it would operate in ambient conditions and add to, but in no way impede, airflow .... even then, it should purely be seen as a method of extracting additional heat from a given size radiator, not as a moneysaving solution.

HTH
Z

doughnutmachine

zeupater wrote: »

Hi

The calculations were based on a convective airflow raised to 45C, therefore a 25C increase above ambient ... how would you therefore reduce the temperature by 30C ??

Anyway .... assuming 45W of heatloss is correct and the reduction could be achieved by sufficiently increasing the airflow then you would need a really powerful fan unit, probably consuming well over 45W ..... remember that the breakeven point from a cost perspective would be based on the differential cost of gas fired heat vs electricity for forced airflow, therefore with a cost ratio of approx 3:1 you would be losing out if providing anywhere over 15W of forced airflow ....

My view is that the radiator booster is a poor solution to a problem ... drawing warmed air and placing the unit on the top of a 70C radiator will likely reduce the design-life of the mechanical components by a factor of 8 (20000Hrs to 2500Hrs), electronics somewhat less, as well as reducing natural convection. Any forced air unit would be better placed below the radiator in a position where it would operate in ambient conditions and add to, but in no way impede, airflow .... even then, it should purely be seen as a method of extracting additional heat from a given size radiator, not as a moneysaving solution.

HTH
Z

sorry i never knew i had to follow your figures? i just thought a rough temp for the back of the radiator would be 50C with a room temp of 20C.....

you seem to assume that the power for the fan would not add to the room temperature as well so your 15W assumption could be described as flawed.....

Nevertheless, we both agree the system doesnt seem to have much merit... unless someone doesnt want the expense of upsizing an undersized radiator

The_Green_Hornet

You have all forgotten the one important factor with these type of gadgets, namely the placebo affect.

Tell someone that it will make their room feel warmer and suddenly they will actually feel warmer.

I've got some invisible ones going cheap if anyone is interested...

zeupater

doughnutmachine wrote: »

sorry i never knew i had to follow your figures? i just thought a rough temp for the back of the radiator would be 50C with a room temp of 20C.....

you seem to assume that the power for the fan would not add to the room temperature as well so your 15W assumption could be described as flawed.....

Nevertheless, we both agree the system doesnt seem to have much merit... unless someone doesnt want the expense of upsizing an undersized radiator

..... then for the temperature behind the radiator to be 30C lower than 50C, ie ambient, the radiator would need to be off ....

Regarding the 15W, that was based on the idea which was raised of reducing the air temperature behind the radiator to ambient and therefore reducing heatloss by 45W, then applying a electricity/gas energy cost ratio of 3:1 ... for simplicity this was a sanity-check exercise which completely ignored that it would be near-impossible to achieve this. To elaborate, but still keep it simple ... if you could reduce the temperature differential by 50%, you have saved 22.5W of heatloss from a gas energy source with a (nominal >45W ?) fan powered by electricity at three times the cost ....
adding all of this complexity does nothing more than the the previous rough sanity check other than coming up with a new simplified cost benefit calculation which looks like (((45x3)-(45x1)-(45x0.5x1))/(45x1)) - resulting in a 50% greater cost than doing nothing, which still has the same result - no saving .... and that's if a 45W fan would do the job.

Whatever size fan would be required makes little difference, it seems to be a ~1.2W DC fan which the boosters have and as previously intimated, a fan of that size would be totally overwhelmed by the natural convection .... it would be pretty logical to conclude that obstructing the airflow behind a radiator would actually increase the temperature of the wall and thus increase the immediate area through-wall heatloss ....

HTH
Z

zeupater

The_Green_Hornet wrote: »

You have all forgotten the one important factor with these type of gadgets, namely the placebo affect.

Tell someone that it will make their room feel warmer and suddenly they will actually feel warmer.

I've got some invisible ones going cheap if anyone is interested...

I totally agree ....

It's quite surprising how many actually try to convince themselves (and others !) that money wasted is money well spent ..... ;)

Z

ps - I've got the invisible ones too, at least I did last time I looked ...

doughnutmachine

zeupater wrote: »

Regarding the 15W

would this 15w fan not provide heat to the room as well....