When should I replace my building's roof top unit?

Demystifying RTU Replacements

The riddle could go something like this, what do you not see, but feel its effects every day;  it’s expensive to keep around but you hate it when it quits. Some of you may be thinking I’m talking about your facility manager, but in reality, this describes your campuses heating and cooling systems.  In the U. S., approximately 60% of these units sit on a building’s roof, with the remainder alongside the building on the ground.The average life expectancy of a large rooftop unit (RTU)  is 20 years. During its lifespan, things like continuous operation, the buildup of dirt, or poor maintenance can impede the mechanical functions. The dampers may begin to fail to open and close. Refrigerant could leak. (Old style refrigerant, R22 is no longer produced and is becoming more and more expensive and so are parts that use R22 refrigerant.) Damage from the elements such as hail, ice, and snow can also wear down your unit/s. This loss in efficiency can greatly increase the cost of running the unit/s in energy dollars; estimates range from a 20%-50% drop in efficiency during the unit’s lifespan.One way to help extend the life of an RTU is to implement a regular preventative maintenance program that includes regular checkups and maintenance and making minor adjustments along the way.  This is far less expensive than waiting for a premature failure to occur.With the help of your trained SFM technician and your facility manager, you’ll know when the unit is reaching its life expectancy and when it would be the most cost-effective to replace it.  When faced with old equipment, there are basically two approaches to replacement; these are PROACTIVE REPLACEMENTS and REACTIVE REPLACEMENTS.On a typical PROACTIVE REPLACEMENT project, you know the equipment is eighteen years old, and your facility manager has advised you that the condenser coils are rotting away. You have time to order high-efficiency equipment with a four week lead time from your national account vendor. The job is scheduled and coordinated and everything goes like clockwork.A typical REACTIVE REPLACEMENT is like fighting a major fire. It usually starts when the unit, that you know is on its last leg, stops working. The SFM technician determines that the unit in question has a burned out compressor. The machine is 18 years old and the condenser coils are no longer efficient. Replacing the compressor would be throwing your money away because the condition of the condenser coils will cause high head pressure for the compressor and you learn that there is a pile of rust under the burners in the heating section. You ask SFM how quickly they can replace the unit with a high-efficiency unit and how much will it cost. Unfortunately, the high-efficiency units with humidity controls that you need have a 4 week lead time.  Now you are in a position where you can’t get what you need on short notice and your building still doesn’t have a functioning heating and cooling system.PROACTIVE REPLACEMENT is advantageous for the following reasons:

• The cost of installation work is sometimes lower.
• There is sufficient time to procure the equipment you want with the factory installed options you require.  (IE a Dehumidification Cycle or Demand Ventilation)
• It's easier to get parts for newer RTU’s.  Manufacturers are required to keep parts stocked for RTU’s less than 10 years old; after 10 years parts are frequently “made to order” which often results in a delay.  It is sometimes difficult to find even “made to order” parts for RTU’s more than 20 years old.
• Work can be scheduled when it has the least impact on building operations and schedules.
• Costs can be budgeted.
• Multiple units being replaced simultaneously can lead to substantial savings.

So how do we know when it makes sense to consider Proactive Replacement?  There are many factors to consider and each institution's particular situation comes into play, but here are some things to consider.

1. Consider time spent on maintenance. When calculating the cost of repairs versus replacement, consider the history of the asset. This history should include its years in operation, preventive maintenance history, and spend for on-demand service over the last two to three years. Based on industry data, a unit that has been in operation for one to five years will cost $100/year on maintenance. However, once the equipment has been in operation for 15 years or longer, that figure triples to roughly $333 per year.
2. Consider the hours/money spent on emergency repair. As mentioned earlier, equipment failures always seem to happen at the most inopportune time—whether that’s when it’s extremely hot out, at the end of the day, or on a holiday or weekend. These emergencies can lead to delays in service and possibly higher hourly rates. Depending on the age of your equipment, this could also lead to hard-to-find parts with excessive lead times.
3. Consider energy costs. Older equipment operates at a lower efficiency than that of new equipment. Even the best-maintained HVAC equipment that has been in operation for more than 15 years will continue to lose efficiency and will never be as efficient as a newer technology that emerges.
4. Listen to the experience of technicians.  Our technicians are looking at hundreds of RTUs per year.  While they can’t predict the future, they can sure develop a good sense of the deterioration level of an RTU.
5. Predictive analysis.  There are more expensive methods for monitoring certain data, to discover changing conditions in RTUs.  They might be worth the cost for very large, or mission-critical units. But because these systems provide their best information in comparison to a benchmark, this technique is best utilized many years before a unit nears the end of its life expectancy.

Knowing when to repair and when to replace middle-aged equipment is never easy.  Use the comments in this article, and discussions with your mechanical contractor and SFM Facility Manager to help with the decision process.