Cross flow fan impeller taken from an air conditioning indoor evaporator unit

Cross flow fan impeller taken from an air conditioning indoor evaporator unit

Recently I replaced an air-conditioning unit at my house because it was too highly microprocessor controlled with inverter for energy savings that the service technician would have to charge me a lot for replacement of the control unit. After thinking about it and considering that he could replace it with a cheaper air-conditioning unit which promises less complicated controls that could go wrong, I opted to change the whole air-conditioning unit.

Volute casing frame

Volute casing frame

That, left me with an evaporator unit and a condenser unit which I could tinker about in my spare time. The problem with the air-conditioning system was that the controls prevented it from running on cooling mode with refrigerant gas in circulation, but it allowed the running of the fan unit.

Volute casing inner shell made of cardboard

Volute casing inner shell made of cardboard

Once I had tested the indoor fan unit that it could be operated, I decided to make use of the cross-flow fan for a project that I had in mind – to exhaust the hot air from the attic of my house. The cross-flow fan had some characteristic of a centrifugal fan and I could make use of it because of its good suction capabilities. Because of its long cylindrical shape, it would be ideal when the suction port is a long, rectangular shape instead of a square – which I could fit into the long, slim windows of my attic, without the need to hack my brick wall. Moreover, it was quiet.

Volute casing cardboard shell glue setting

Volute casing cardboard shell glue setting

In order to make use of this fan, I had to fabricate some sort of ducting for it. Also to maintain the efficiency of the cross-flow fan design, I needed to fabricate the ducting to follow the volute shape as far as possible.

My plan was to hang the fan unit near to the ceiling where all the hot air was supposed to be. By convection for the room, hot air rises and cold air would come down. The suction would be taken from the edge of the fan at the top as per normal air-conditioning inlet. However, the discharge of the fan, which would normally be blown into the room would have to be ducted out to the outside of the building. In this way, the fan would act like an exhaust fan.

Volute casing edges glued in place

Volute casing edges glued in place

The challenge was to fabricate the ducting so that it would match the dimensions and locations of the window at one end and to be connected to the discharge end of the fan without any loss of air at the other end. All the gaps had to be sealed so as to maintain its efficiency.

A frame forming the skeleton had to be made out of strips of wood. Plywood was used to at both sides, cut to the required shape. There were some adjustments and trimmings to be made to ensure that the parts could fit into the existing shape of the fan housing. Some parts were screwed in place to make sure they don’t fall off, while others were glued in place.

Corrugated cardboard was used as the skin of the fan ducting as it was easy to work with and the pressure was not expected to be high. All the seams and gaps were sealed off with masking tape.

That was the fabrication part. Now came the installation part.

Exhaust fan made from crossflow fan

Exhaust fan made from crossflow fan

As the fan was originally an indoor evaporator cooling unit, it would be hanging on a plate which was installed on the wall. I had saved the hanging plate for this purpose, so it was just a matter of installing the hanging plate at the correct location in relation to the fabricated ducting and the location of the window. Well, this was done correctly.

Next, I had to seal off the ducting where they were attached to the window. There were some gaps because the actual shapes were not exactly as what I had fabricated. Some gaps were large. I cut out pieces of cardboard to the shapes to be covered and then seal off the gaps by masking tapes. In this way, all the gaps were effectively sealed off so that whatever air being sucked by the fan would not find their way back into the room.

Then it was testing time.

At the time of the test, it seemed to be able to reduce the room temperature by about 1 or 2 degrees Centigrade.