Condenser fan speed controllers......
I have installed many, and if you have too you will likely be very happy with the results. The really sort out a lot of problems.
If installing , always make sure they are installed measuring latent pressures on the receiver or the liquid line as they work far more accurately rather than a simple head connection.
The advantage of using this type of head control , is that the fan will slow down and speed up to maintain preferred condenser saturation temperatures. This also eliminated condenser shock by low ambient temperatures and "cycling" fans that can cause a sudden low pressure at the condenser which will draw back or reverse flow in the liquid line pumping down the unit by starving the evaporator. (a liquid balance line usually fixes that problem)
Using a VS fan head control makes a system perform better by a constant pressure drop across the TX valve. This ensures maximum performance when setting superheat. It also keeps subcooling in the condenser constant.
And guess what else remains constant... The compression ratio.
The only unfortunate downside to using one of these is that you lock the compression ratio all year by setting your saturation temps in the condenser to a permanent design temperature, This means that in low ambient weather , you are artificially re-designing the condenser TD to a higher value which creates a new tangent for a low ambient design which never existed (see the chart curves).
So your power consumption, port head temperature on the discharge valves remain the same, where as normally it would have lowered in lower ambients. Now this might cause some superheat deviation in the evaporator but low ambient... low problems really with load. It would have also offset more power consumption and lower discharge heat.
However folks. If you decide to use one, try not to oversize the condenser thinking this will solve your low ambient problems with a high ambient condenser design. These days of heat are far and few between. My chart has been sized for a 10K design with a 40.c ambient and a maximum condenser saturation of 50.c to show how far out it can get on an 18.c day..
These VS controls for the fan motor are best used where indoor loads are high in low ambients or for very critical humidity design.
Images of VS controllers from the products @ www.danfoss.com
Caution with using evaporator pressure regulators.
Firstly, I am a fan of them, they are problems solvers!. They make your day perfect and set the saturation temperatures final. The ability to lock humidity in a coolroom by locking the final evaporator temperature difference. Changes in condensing temperatures do not create problems with floating evaporator pressures.
But.... If you fit one, make sure that the system is well matched for capacity , meaning the outdoor and the indoor are ideally suited as a one to one system. If used in a multi-temp system with larger compressors operating more than one indoor, you must make sure that the system can unload.
If not, you will cook your compressor, run up the amps, decrease volumetric efficiency and increase the heat of compression.
The picture below shows the problem faced by excessive compressor displacement by being too large.
Caution always recommended.... good system design a must..
Check out my YouTube Video
DO you know what they do and how the work?
Many will soon
DId you know that these are easy to test but so misunderstood..
These high/low and universal transducers are not just to act as safety devices on larger single ducted / multi AC and VRV/VRF multi.
Depending on the logic algorithms of any brand manufacturer AC's operating computer , they can create unusual problems when faulty, but in fairness make a unit work excellent and cost effective when they are normal.
If transducers are out of calibration by fault, they can prevent loading up (ramping) of inverter compressor or staging of constant speeds, false low gas fault warnings , reversing valves that do not engage in heating mode (because they use the low pressure transducer to show positive pressure displacement for RV gate change at a given RPM) and failure of indoor unit EEV's to open up and feed refrigerant. They set saturation temperatures for both heating / cooling modes and maintain them at a constant.
And.. if you have a multi outdoor condenser , there are many of them that might cause it.
Yet they are easy to test and diagnose. All you need is a manufacturer pressure/voltage chart (found in a service manual) , a set of gauges and a DC voltmeter. Then you can test them in seconds!!!!!!!!!!!!
Check out my YouTube Video on DC motor testing on split systems
PWM - pulse width modulation
We cant see it with our eyes... A voltmeter shows a lower or higher output voltage to the load and we just know its a dimmer switch. Hey its more than that.
Its a duty cycle control, maintaining the source power constantly but changing the switching speeds and this is what drives inverters. Too fast for us to see... but not for the oscilloscope.
Imagine switching both positive and negative feeds to create a sine wave , then chop the same feeds twice more at differing time intervals and you have 3 phase inverter output from one single phase DC supply.
Folks ... don't beat your brains out. it is just that simple to do. You see here you are looking at one positive signal switching which we call DC. No negative signal other than 0V. But give it a negative switch and it looks like a raw AC waveform. This is the basis of phase creation from +/- DC
You see an inverter gets to do both at the same time... And the world just got smaller for all of you , nothing is over complicated. Its just ON - OFF high signal, low signal positive on and negative on.
PTC - Compressor starter - Positive Temperature Co-efficient
Hey, simplicity works but it has its limits
The most cheapest compressor starting device, and can I say it is not a relay , more a resistive switch.
For very small class capillary system refrigerator, usually a bar fridge or cubic fridge enter the PTC.
Now these are not high tech, and they need to have decent intervals in time before starts so they can cool down.
Also the system must equalise pressure between the high and low sides to allow for a low compression start.
The PTC starter is similar to the potential relay not by design but where the start winding is engaged immediately from first power up. . At start up the PTC is cool and has no opposition to current flow by a preset low resistance which is in series with the compressor start winding.
The compressor starts by resistive start and induction run, as the current flows through the PTC , it heats up increasing its internal resistance until it will not allow more current to flow , disengaging the start winding. The start winding is isolated and will not engage further as a trickle of current to the start winding will maintain heat and high resistance during the operation of the compressor.
When the unit stops the PTC MUST!!! cool down to allow current to flow again on next start-up. If it trys to start to early the internal overload will activate in the compressor.
So it really is not designed for frequent starts and requires very low starting torque.
Don't expect too much , price and capacity dictates control, yet I do like how simple these are.
The PTC is small, no bigger than a 10c (Australian) coin and as about 4mm thick.
Note also the compressor terminals are inverted to this design as per the Danfoss types. I have marked them.
These starter types are typically only used on low capacity, low torque compressor where off cycle pressure equalisation occurs , as you see in capillary systems
Now does anyone see a Star Trek logo on the PTC relay disc in the pictures above? , or am I just seeing things :D
Check out my YouTube video on inverter testing a small Daikin Split outdoor unit
Check out my YouTube clip
The most important part of the system is the restriction of flow.
The compressor prevents back-flow and maintains pressure against the restriction which could be a capillary tube or expansion device orifice.
It is a venturi effect..... The most amazing part of thermodynamic transformation , without which we have no separation of saturation temperatures.
This is for the apprentices to review from their first week back and to step into the greater world of refrigeration we live in.
I'm always fascinated by the simplicity of this design to achieve a manipulation of energy to create a heat transfer effect.
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