Fan Speed controller for condenser fan

[tadipatrir]

Hi,

I am building a condensing unit for medium temperature application. In this I will be installing a fanspeed controller (pressure based) - Saginomia make for condenser fan motor.
I was wondering where to tap the discharge pressure from -

a) In the discharge line
b) Receiver
c) Liquid line

I consider discharge line as it represents the actual pressure to be dealt with by fan motor. On the other hand liquid line and receiver will have the stabilised condensing pressure which is an actual value directly in relation to the ambient.

Can experts of this forum suggest me in this regard?

Best regards

[mohamed khamis]

I suggest at the end of discharge gas line (inlet to the condenser) and if u have acute gas pulsation, u should put muffler to dampen these pulsation a way of pressure sensor reading. the benefit of discharge gas end line is to be a way of any pressure variations during valve opening/closing. yes the pressure reading at the liquid line and receiver is quite stable but u have to take the effect of the pressure drop for condenser and liquid line auxiliary components because the pressure drop in liquid is more significant than for gas. In addition, if there is back flow of liquid inside the condenser this can raise up the condensing pressure without any sensing of the liquid line pressure sensor.

Cheers

[tadipatrir]

Thanks for the reply. Iwas also thinking that discharge line is more relevant.

Regards,

[Camille]

you can tap in into the high pressure compressor discharge line, or to the hp pressure discharge tube line on your gauge board, if you have a PLC system you could install an analog pressure transducer [Ashcroft or Danfoss] or a mechanical type dry contact as a Johnson Control switch, [see my attached sketch

Regards
Camille [Canada]

[BESC5240]

Hi all,

Just 2 things:

1) Remember why you want to use a fan speed controller : it's to keep a minimum (stable) pressure before your expansion valve (or in the liquid receiver). So you put your pressure connection of your controller on the receiver !!! or just between condensor and receiver.

2) Guideline n° 1 : RTFM : in attachment you will find an extract of the Saginomiya RGE data sheet : ideal connection = liquid side.

Connection to the discharge line is allowed but:
- you're not interested in the discharge pressure, but in the liquid pressure (and yes there can be a difference)
- gas pulsations and condensed liquid in discharge lines (or trapped liquid/oil in pilotlines in discharge line) have been known to break a few pressure controllers in discharge lines.

Best regards

[mohamed khamis]

Hi all,

Just 2 things:

1) Remember why you want to use a fan speed controller : it's to keep a minimum (stable) pressure before your expansion valve (or in the liquid receiver).

Yes but this is not only reason to use the fan speed controller otherwise what is the difference between it and head pressure controller both of them do the same function in terms of providing the adequate the condensing pressure to TXV but the fan speed controller has another privilege which is the economy factor of energy saving in fan power. Therefore if our interest is the energy saving the probe should be installed in the discharge line (with considerations of gas pulsations or unsafe operation of the controller) because the liquid line pressure differs from condensing pressure particularly at low ambient temperature the condensing pressure drops drastically and this reinforces the inertial pressure drop inside the condenser due to the wide difference in two-phase densities. this stretches out the difference between the condensing pressure and liquid pressure and the fan speed is adapted according to value less than is the optimal corresponding to the actual condensing pressure. However, if the installation in discharge will cause troubles in controller operation as u mentioned so it is better to be installed in the liquid line irrespective of the energy saving gain.

Cheers



Best regards:)