Getting Ready for the Cooling Rush

Thanks!

First of all, thanks for the kudos on the heat pump book... Glad you are enjoying it. I had a blast writing it.

Secondly, I have absolutely no problem starting up an air conditioning system during cold weather, providing that the technicians that are doing the work have been properly trained to do so.

Here are a few things to keep in mind.

Design conditions are 95 degree outside air temperature, 75 degree indoor air temperature at a relative humidity of 50%.

If we are able to simulate these conditions as closely as possible, the chances of our startup being worth more than 2 cents is greatly increased.

It's relatively easy to simulate these conditions, if only for a relatively short period of time. First, crank up the heating system to put some load on the house. People have expressed their concerns about this as taking to long to do in the course of a routine startup, but here'st he trick. Give your customers a call about an hour before you get there and ask them to turn their thermostats up to 77 degrees. By the time you get there, there will sufficient heat load on the air conditining equipment when you arrive.

Have your technicians take a reading of the relative humidity in the home using a sling psychrometer to read the dry bulb and wet bulb temperatrures in the space. An RH close to 50% is great, but don't freak out if it's not.

An Rh below 50% means that our delta-t across the evaporator coil will be greater than the typical 17 - 20 degrees, while an RH above 50% means that our delta-t across the evaporator coil will be lower than the typical 17 - 20 degrees.

Now to the outdoor unit.

Blocking a portion of the condenser coil is not a bad thing. Many have said that this is not an effective mean by which systems can be started up in the cooler months. Such is not the case. Fan cycling, shutters, condenser folloding all operate on the concept that reducing the effective surface area of the heat transfer surface (condenser coil, in this case) will increase the sondenser saturation temperature and pressure in an attempt to maintain the condenser saturation temperature and pressure at the desired level. So, block away but do so carefully.

If the system is operating with a fixed bore metering device, the refrigerant charge can be evaluated by a combination of the evaporator superheat, condenser subcooling, and the delta-t across the evaporator coil.

THE NUMBER ONE TIP FOR STARTING UP ANY AIR CONDITIONING SYSTEM IS TO VERIFY AIRFLOW BEOFRE DOING ANYTHING TO THE SYSTEM.

During the winter months, homeowners may close off some suply registers to avoid overheating during the winter or may not have cleaned the air filter. Improper airflow acrosst he evaporator coil can cause the technician to inaccurately conclude that there is a system malfunction that requires expensive repairs.

More to come.

Hope this helps.