It is not uncommon to find packaged and split system air conditioning units on the Phoenix market that have been in use since the 1970s or 1980s. Because the average life expectancy of this type of HVAC equipment is around twelve At fifteen, it’s time to retire some of these tired old workhorses.
An added bonus when replacing older air conditioning systems can be a significant increase in energy efficiency with a concomitant decrease in energy costs. With the amount of discussion we’ve been hearing in the news lately urging us all to go green and save energy, it probably won’t be an unpleasant consequence.
Along with the good news of saving energy, there are also some considerations that the competent air conditioning contractor will share with you when it’s time to replace older equipment. I would like to share some of them with you. Let’s first discuss split system heat pumps and then briefly cover things that are common to both package units and split systems.
As SEER (Seasonal Energy Efficiency Ratio) ratings for new air conditioning equipment increase, HVAC industry practices that have been marginal in the past will no longer be acceptable. One such unacceptable practice occurred whenever split system heat pump condensing units were replaced. Common practice in the past was to replace the heat pump condensing unit without first verifying that the new condensing unit was compatible with the old air handler. Various problems can arise whenever there is a mismatch between the condenser and the indoor air handler.
The first problem is the reduced efficiency that will result from replacing an older condensing unit without replacing the air handler at the same time. The reason for this is that air conditioner manufacturers do not rate current model heat pump condensing units with “old” air handlers that are twenty years old. To achieve the published SEER, a heat pump condensing unit must be paired with an indoor air handler or fan coil unit with which it has been rated. In other words, if you install a new 13 SEER condensing unit with an older 8 or 9 SEER air handler, the actual efficiency achieved will be less than 13 SEER.
A second concern is that there may be a discrepancy of internal coil volumes between an older air handler and a newer condensing unit. Since minimum SEER mandates have required higher efficiencies over the years, manufacturers have made upgrades to both indoor and outdoor coils to increase heat transfer efficiencies. Newer condensing units may have a different internal coil volume than some of their older counterparts. If a new heat pump condensing unit is installed on an old air handler, it may result in improper operation in heating or cooling mode which will require seasonal refrigerant charge adjustments and unnecessarily increase service costs. It can also contribute to system reliability issues.
A third problem that we all face is the difference in the characteristics of refrigerants and compressor lubricants used in new systems. Since new air conditioners using R22 refrigerant cannot be manufactured after 2010, major manufacturers have already started making newer high-efficiency models using R410a refrigerant and polyol ester (POE) oils. The new refrigerant has properties that are very different from R22, which has been the main refrigerant for split system and combination air conditioning systems for decades. In short, R410a is not compatible with refrigerant flow control devices in older air handlers that were designed for R22. Even if the flow control device could be changed, problems can still arise over time if the original mineral oils are not properly cleaned from the system.
A fourth consideration is the size of the refrigerant line. New high efficiency R22 condensing units often require larger diameter vapor lines than originally installed with the old system. It may not be economically feasible to replace the vapor lines, so there will be efficiency losses as a result of the higher refrigerant pressure drop in the smaller than recommended vapor line. A possible solution to solve this problem would be to install a new R410a split system condensing unit and a new R410a air handling unit. Since R410a generally requires smaller vapor lines than R22, it would allow the use of existing smaller vapor lines. The recommended procedures for removing residual mineral oil from existing lines should be followed if conversion to R410a is implemented.
When all of the above factors are taken into account, it becomes clearer that the best course of action is to replace the indoor unit along with the heat pump’s condensing unit. While this is more expensive up front, it can help avoid significant problems later.
Now that we’ve discussed issues unique to split system replacements, let’s consider a few factors that are common to both pack units and split systems.
A problem that is common to both package units and split systems in higher SEER products is reduced cooling capacity at higher outside temperatures. This can be verified by checking the manufacturer’s ratings for the old A/C system and the new A/C system at outside temperatures above 100 degrees. Newer high-efficiency systems generally tend to lose sensible cooling capacity more quickly than lower-efficiency units manufactured in the past. This is an important factor when evaluating an existing system that is doing only a marginal job of cooling the space it serves. A new system may need to have a higher capacity to produce the desired cooling effect at the higher outside temperatures we see in Arizona. There is a caveat with this as well. You also don’t want the replacement system to be too large in size or it won’t work as intended.
Another thing you’ll notice is that many of the newer systems have larger cabinets than the older style units. The larger cabinet size can become a problem in confined areas. Since minimum clearances must be maintained, a new system may not fit where the old system was installed. This consideration will be unique to each specific application, but you should be aware of it so you don’t get a nasty surprise.
One final item to consider regarding split or mixed system replacements is the significant difference in equipment costs. Greater efficiency comes with a higher price tag. Based on a leading manufacturer’s price for a 5-ton package heat pump, the jump from 10 SEER to 13 SEER comes with a price difference of over 30%. If it’s been a while since you’ve had an air conditioning system replaced, you may have “adhesive shock.” Material price increases coupled with the use of advanced technologies such as variable speed compressors, dual compressors or discharge scroll compressors along with variable speed fan motors and improved control systems all contribute to increased equipment costs. Keeping this in mind when projecting future costs for HVAC equipment replacement can help you develop more accurate replacement quotes.
