Question from another forum:

We have a split system for heating. Is it more economical to run higher temp and lower fan speed or lower temp and higher fan speed?

Rule 303 said:

Question from another forum:

We have a split system for heating. Is it more economical to run higher temp and lower fan speed or lower temp and higher fan speed?

I suspect the former. Moving air by a fan runs on a cubed law. Double the amount of air moved and eight time the energy is required.

I would say the later. Higher fan speed will get what heat is available out into the space better, and the lower delta T will be more efficient in the creation of the heat and will means loss of heat in the room will be lower as well.

Not sure whether this will help, but for cooling we were told that the humidity needs to be removed from the air and that the best way to achieve this was to to run the fan at its lowest speed. Perhaps the opposite would be true for heating.

Stealth said:

I would say the later. Higher fan speed will get what heat is available out into the space better, and the lower delta T will be more efficient in the creation of the heat and will means loss of heat in the room will be lower as well.

Tis a reasonable point, Stealth :)

I’m coming from an area where it is all cooling and lower fan speeds definitely lower energy usage. In that case there really isn’t a delta T as you are trying to keep T constant.

In heating a house I suspect there will be a funny shaped curve (engineering speak) where having a low ambient temperature as your initial starting point will mean that getting up to a required T (almost infinity in the case of Alex) will require higher fan speeds, whilst once the equilibrium temp is reached a lower fan speed with a higher element temp may be advantageous.

Excellent….

I recall asking a similar question of the scientific people at a large solar water heating manufacturer – optimum flow through a collector for a given temp difference (water:ambient). They had NFI. Not even the first clue on how to calculate it.

Rule 303 said:

Excellent….

I recall asking a similar question of the scientific people at a large solar water heating manufacturer – optimum flow through a collector for a given temp difference (water:ambient). They had NFI. Not even the first clue on how to calculate it.

I had this dicussion about solar collectors as well. once again it is a comprimise between the delta t and the power loss with the circulation pump. Generally faster flow (up to a point) will be better. But there are other considerations as well like flow noise and cost of higher pressure pipe/fittings.

Stealth said:

I had this dicussion about solar collectors as well. once again it is a comprimise between the delta t and the power loss with the circulation pump. Generally faster flow (up to a point) will be better. But there are other considerations as well like flow noise and cost of higher pressure pipe/fittings.

The pressure in the system is controlled by a valve on the return side. The pump needs only to lift the water to the top of the system. The pressure drops dramatically as the water runs through the collector matting, as you would imagine, then picks up again (to original pressure) in the return-side collector manifolds, pressure in the system after this point is controlled by the valve.

Depends maybe too if you are including mixing/equalization over whatever air mass. If not then probably the former.

A night ….

http://www.youtube.com/watch?v=EuN7V5LOZiw