The most difficult service call to deal with is when it is extremely hot outside and you arrive at the customer’s home and they are upset because the system will not keep up. So, what do you tell them? First, let’s look at the following:
During the refrigeration cycle, liquid refrigerant from the condenser carries heat back to the metering device. Any heat carried back to the metering device wastes system capacity. The net refrigeration effect is determined by subtracting the enthalpy (Btu per lb. of refrigerant) of the liquid refrigerant from the enthalpy of the suction vapor. Basically, the higher the temperature of the refrigerant arriving at the metering device, the lower the net refrigeration.
Capacity problems arise when the condenser cannot reject enough heat due to extremely high outdoor air temperatures. As the temperature of the air entering the condenser rises so does the condenser pressure and the condenser's performance diminishes. With hotter liquid leaving the condenser, the result is lower system capacity for the customer.
What do you tell the customer?
First, you must understand how systems are designed. Most areas of the country have what is called a Summer Design Temperature for air conditioning. The average summer design temperature for most of Florida about 93°F. A properly designed system should be able to maintain an indoor temperature that is 20°F cooler than the Summer Design Temperature.
This means that a home in Florida should maintain 73°F indoor air temperature when the outdoor temperature (at the condenser) is 93°F. But, what happens when the outdoor temperature at the condenser is 98°F? The system can only maintain a 78°F indoor air temperature. As the day progresses the indoor temperature will begin to creep up and the system is running non stop. This is when the customer calls!
There are three things to remember when you address this issue:
Since high head pressure is the problem, the solution is simple, lower the head pressure. By placing a lawn sprinkler next to the condenser, the head pressure instantly drops. This results in cooling liquid leaving the condenser and increasing the net refrigeration effect.
Notes:
by Ron Walker
During the refrigeration cycle, liquid refrigerant from the condenser carries heat back to the metering device. Any heat carried back to the metering device wastes system capacity. The net refrigeration effect is determined by subtracting the enthalpy (Btu per lb. of refrigerant) of the liquid refrigerant from the enthalpy of the suction vapor. Basically, the higher the temperature of the refrigerant arriving at the metering device, the lower the net refrigeration.
Capacity problems arise when the condenser cannot reject enough heat due to extremely high outdoor air temperatures. As the temperature of the air entering the condenser rises so does the condenser pressure and the condenser's performance diminishes. With hotter liquid leaving the condenser, the result is lower system capacity for the customer.
What do you tell the customer?
First, you must understand how systems are designed. Most areas of the country have what is called a Summer Design Temperature for air conditioning. The average summer design temperature for most of Florida about 93°F. A properly designed system should be able to maintain an indoor temperature that is 20°F cooler than the Summer Design Temperature.
This means that a home in Florida should maintain 73°F indoor air temperature when the outdoor temperature (at the condenser) is 93°F. But, what happens when the outdoor temperature at the condenser is 98°F? The system can only maintain a 78°F indoor air temperature. As the day progresses the indoor temperature will begin to creep up and the system is running non stop. This is when the customer calls!
There are three things to remember when you address this issue:
- All systems, when operating at outdoor air temperatures above their design temperature do not provide enough cooling.
- It is not a mechanical problem.
- You can temporarily increase capacity, although it is not recommended.
Since high head pressure is the problem, the solution is simple, lower the head pressure. By placing a lawn sprinkler next to the condenser, the head pressure instantly drops. This results in cooling liquid leaving the condenser and increasing the net refrigeration effect.
Notes:
- The volume of water must be adjusted to maintain proper head pressure.
- Using water with high mineral content is not recommended.
- Only use this procedure when absolutely necessary and during the hottest parts of the day.
by Ron Walker