IN COOL WEATHER CONDITIONS.
- Weather conditions are rarely the optimum 85° when you need to set or check a charge.
- For companies with many service contracts, there is no practical way to wait for ideal weather before performing system maintenance checks.
- Tenting is a pain in the posterior, takes a lot of time and doesn’t work all that well.
- Cool weather conditions result in several problems associated with checking or setting refrigerant charge.
- There is little or no cooling load which results in low head pressure.
- Even if there is some load and some usable head pressure, there is a further pressure reduction when the refrigerant gas reaches the condenser because the condenser fan blows the cool air across the coil. Thus the refrigerant gas immediately turns to liquid.
- Because the gas quickly turns to liquid the inability of the compressor to build usable pressure is magnified.
- The liquid refrigerant is subjected to the cool air blowing over the coil.
- By the time the liquid refrigerant leaves the condenser it has reached a temperature close to the outdoor air temperature.
- If allowed to operate during these conditions, oil flow is reduced, slugging is almost assured. Either of these conditions can ruin the machine.
- Computer rooms, kitchens, some industrial shops generate heat which gives the air conditioner enough load to allow the machine to run in cooler weather than say a residential system.
- However, when the outdoor temperature gets cool enough, depending on the heat load, even these systems need assistance in maintaining head pressure. That’s what the FanHandler LA-277 was designed for. It has a lot of other uses.
It’s a cool day (say 50 to 55°) In order to check an air conditioner’s charge and operation, you have to fool the machine into thinking that it is a nice 85° day. That means you need a heat load for the air conditioner to work on. The simple solution to that is to turn on the heat. Next you need to control how fast heat is removed from the hot gas that reaches the condenser. Simply control the speed of the condenser fan. About 105° is a very good temperature for the liquid refrigerant leaving the condenser. So any time that the liquid temperature is lower than 105° the condenser’s fan must be slowed so that heat removal from the refrigerant will slow down.
For the “purists” among you, If you don’t like 105° liquid temperature, move the sensor further away from the condenser, or clip the sensor to one of the motor brackets to measure discharge air, or just use the minimum speed pot to get whatever fan speed you want and forget the sensor.
- One of the first low ambient strategies that I stumbled onto was a flooded condenser system. This system had an extra supply of liquid refrigerant. The control system regulated the level of refrigerant in the condenser. As the outdoor air got cooler and the head pressure started dropping, the extra supply of liquid refrigerant would fill the condenser coil to a level depending on the head pressure. Thus reducing the amount area/volume of coil containing refrigerant gas exposed to the air blowing over the coil. On cold days, the condenser was almost full of liquid. Head pressures were held and it worked fine. However it was a bear to work on and I doubt if I’d have either the ability or patience today.
- In the early 60’s we developed the solid state Fanhandler to control direct drive blowers for heating systems. These controls smoothly regulated blower speed from an adjustable low speed at 75° to full speed at about 135°.
- Next, “heating only” heat pumps were developed and we were asked to modify the temperature range from 75° minimum to about 115° full speed to allow for rapid head pressure build up, thus discharge air temperature increase. At the same time, we kept head pressures from going through the roof by achieving full blower speed at the lower temperature of 115°.
- On a cool day in the early 70’s, I was charging a system, with internal heat gain. I was wrapping garbage bags around the condenser. I knew that about 105° discharge air out of the condenser was about right for a nice summer day. I hooked up one of our heat pump controls and charged the system. That led to thousands of LA-240’s being sold for low ambient control of computer room equipment and even more being sold as a tool for cool weather checks and charging.
- There have been a lot of copy cat controls that try to do the same thing as the LA FanHandler controls. Some turn the condenser fan on and off from pressure. My personal opinion on this method is that it can tear the guts out of the machine. Some try to control from the point where the refrigerant gas and liquid meet. This is a moving target which also results in surging. I’ve not seen a one that doesn’t surge up and down which I believe is also harmful to the machine.
- The LA-120 (special low temp.) Is used by one of our OEM customers (Sunteq Geo) to control the speed of a ground source heat pump’s circulating pump. It is used to control head pressures just like the LA-240 is used for standard AC. This is especially important when the system is switching between heat and cool. Works best with Grundfos pumps.
- The LA-120 or 240 (special order - Speed range = 80 low - 100 full speed) is also used to control attic ventilation fans and used in solar applications where the south wall is used as a heat-gathering plenum.
- The LA-277 can be used on commercial systems where 440 volt 3 phase supplies the system and one leg of the 440 to ground (277) is used for the condenser fans.
503-623-8766 - www.fanhandler.com