Coil cleaning is a much needed service for any customer - residential, commercial, industrial, healthcare, educational, etc. Coils are everywhere from evaporator, to condenser, reheat, heat recovery, heating, process, chiller, cooling towers and refrigeration.
Cleaning is an ongoing process (repeat business) – coils are getting dirty during everyday use, due to improper installation, inadequate pre-filters, no filter, leaking filter racks and dirty operating environments. Some coils need monthly, quarterly or yearly cleaning – depends on the operating environment.
Dirty Impacted Coils Can Lead To:
- Replacement of the coil sets
- Increased run time on HVAC equipment
- Inefficient operation of the chiller – Excess wear and tear on chillers
- Loss of compressors and fan motors - Stress!
- Guaranteed to increase your energy use
- Provides very poor indoor air quality (IAQ)
- “Dirty Sock” syndrome
- Microbial and bacterial growth (Humidity) – hinders the water shedding ability of the coil
- Improper airflow to occupied spaces
- Improper temperature delivery
HVAC is typically 50% or more of a facilities monthly energy bills. There should be a big incentive to keep these systems running at peak performance and efficiently to minimize energy cost.
Why does my client care?
There is a direct verifiable return on investment for coil cleaning as proved by the following ASHRAE study:
The 34-story building in NYC has 1.2 million square foot of floor space which has to be cooled from 6 am to 6 pm using four large 30-year-old air handlers:
- SF-6: 250 tons, 880 kW
- SF-7: 123 tons, 433 kW
- SF-8: 121 tons; 425 kW
- SF-9: 81 tons; 285 kW
After testing during the first control week, SF-8 and SF-9 were taken offline for two days to perform a modern deep clean on both air conditioners. The two systems were then put back into service and tested in exactly the same manner for a further week afterwards.
In all, HVAC inspectors and TAB contractors continuously measured 54 different data points from the two air con systems for a week before and a week after cleaning, including:
- Coil differential pressure
- Air and water temperatures
- Condensate temperature
- Supply air velocities
- Outside air temperatures
- Volumetric flow rates
- Voltage and amps
The ASHRAE study found that cleaning each system decreased coil differential pressures by 14%, which produced a corresponding increase in the flow rate and overall cooling capacity of the system by the same amount
After cleaning, the smallest air conditioning unit of the four – SF-9 – started punching well above its weight, adding an extra 19-22 tons of cooling capacity (an additional 67-77 kW), increasing its overall capacity by a massive 25%.
The thermal efficiency of the cooling coils in the cleaned systems increased by 25%, and condensate water temperature dropped from 3-4°C before cleaning to 1-3°C after.
The inspectors estimated that 100 tons (352 kW) of cooling capacity would be added to the building once all four air handlers had been cleaned and restored in this manner.
Based on year-on-year HVAC building costs, ASHRAE estimated that cleaning one of the air handlers resulted in efficiency improvements that will lead to energy savings of up to $40,000 each year.
The Hidden Enemy:
Biofilm growing deep inside the coil sets are the hidden issue, it’s easy to make a coil “appear” clean and shiny, but what’s going on deep inside the matrices?
A complex microbial matrix growing on coils and drain pans
- Composed of different microorganisms adhering to surfaces and producing polysaccharides, proteins and nucleic acids
- Allows the biofilm to stick together and develop attached communities
- Life in a biofilm provides protection from penetration of outside agents such as antimicrobial agents.
Why does this matter?
Biofilm acts as an insulator on the coils surface affecting the temperature and airflow. It does not take much buildup to alter the operation of the coil.
- 0.006 in/150 microns = 5.35% increase in energy consumption
- 0.012 in/300 microns = 10.8% increase in energy consumption
- 0.024 in/600 microns = 21.5% increase in energy consumption
- 0.036 in/900 microns = 32.2% increase in energy consumption
Note: A human hair is approximately 100 microns
Biofilm by products:
- Volatile Organic Compounds (VOCs)
- Microbial Volatile Organic Compounds (MVOCs)
- Known opportunistic organisms causing infections
- Sick Building Syndrome
- Occupant complaints
- More sick days used due to allergy/cold like symptoms
Biofilm is not a new problem, science and research have exposed it as being a more common occurrence than previously thought.
Prevention: Proper filtration in place before the coil sets – fix leaks, gaps in filters, gaps in filter racks, pre-filters needed in some cases, pleated filters best bet.
Cleaning: Regular cleaning from the time it is put in service can go a long way to preserve your expensive coil sets. In fact regular cleaning and inspection can solve most of the issues discussed in this article.
Treating: There are products designed for treating the drain pans and some spray applied to the coil sets, these products include something to inhibit biological growth.
How do I get started cleaning coils?
It is not very expensive to get into coil cleaning, proper training of your crews is crucial. Some coils can be cleaned with nothing more than a garden hose, some coil cleaning chemicals and a spray wand.
Larger thick coil sets will need more attention requiring higher pressures and water flow to rinse, hot water or steam, chemicals and careful water control.
Time is the real factor in cleaning, chemicals need dwell time, rinsing to restore a coils performance takes a large amount of time. No fast solution.
Restoring a coils performance through cleaning is not something you should include on your PM schedule, the time taken warrants additional charges. We have had large (400 ton) coils that needed 3-4 deep cleanings in a few month’s time to restore the performance.
Some of my favorite tools for cleaning:
- Foaming coil chemical application gun
- Long coil wand/lance with a spray jet on the end – great for cleaning condensers without disassembly.
- Water containment devices
- High flow, low pressure power washers – allows for high volume of water for rinsing.
Science is changing at all times, the harsh chemicals we used to use years ago are now frowned upon and research has shown that they were doing damage to the coils construction and drain pans. With many new higher efficiency coil sets being made from mixed metals I prefer to use a metal safe chemical – safe for all metals.
There is also a probiotic cleaner and treatment being produced to address the biofilm issues that are resistant to other chemicals. Science is making it easier to do a thorough job.
- Coils are everywhere
- The need for cleaning is ongoing – always getting dirty
- The need is often overlooked during budgeting
- Dirty coils are costing facilities lost money, cfm, temperature and occupant comfort
- Cleaning is not particularly difficult – proper training a must
- Science is catching up – better, safer cleaning agents
If you have any questions please contact Robert Rizen, ASCS, CVI , Technical Trainer at 314-972-2067 or firstname.lastname@example.org.