Heat Recovery:  It's There, Why Not Use It?

In our experience, most plants are letting one of the best energy saving benefits of compressors fly out the window.  The heat level inside of a compressor room is typically a challenge to keep under control.  If the compressor room gets too hot, it can play havoc with your equipment.  Air cooled compressors typically run discharge temperatures of 100-110°F above the ambient conditions in which they are sitting, and the approach design for the aftercoolers is typically about 15°F, meaning the air leaving is about 15°F above ambient.  A 100°F compressor room will cause  compressor  discharge temperatures to increase into the 200°F range, which could shorten the life of your lubricant, and the discharge air from the aftercooler will be soaring above the 115°F mark.  This will cause dryers to underperform, sending wet compressed air into your system. 

The historical answer was to attach ductwork to the compressor and send the heat outside.  Some did see the value of recovering the heat and included a simple manual louver to direct the heat into the facility in the colder months.  The problem with manually actuated louver systems is that they are manual.  Did someone forget to switch it?  During the spring and fall, the heat may be needed at night, but not during the day.  It is typically deemed a hassle so most keep it directed outside and run the heaters inside if required.  Some complain that the heat coming into the plant is too hot and will change it to outside but then never change it back.  When you exhaust outside, the cooling air is pulled from the compressor room and creates a negative pressure in the compressor room.  Most will prop a door to the plant open in the winter because the incoming louvers will bring the temperature in the compressor room below freezing.  This brings the air you have just paid to heat in your plant into the compressor room, where it is used to cool the compressor and then dumped outside.  Make up air for the plant is then drawn in through open doors to the outside, perhaps leaking through windows or increasing the load on your make up air units.

Why consider Sullair’s EES (Energy Efficiency System)?

IAC’s approach to designing air systems always includes energy efficiency considerations.  EES is another part of our overall savings package and works by converting exhaust from the air compressor into a usable source of heat. A thermostatically controlled damper package controls the heat being directed into the building when required and expels it to the outside when not required automatically.  Plus it uses 100% outside air to cool the compressor, ensuring that when the heat is needed, it is introduced as positive pressure to your facility.

With EES, Rising gas Prices Mean Rising Savings

Cost of gas is on the rise year after year.  We are approaching $0.90 per therm in the Midwest.  So what kind of savings are we talking about here?

In Cincinnati Ohio, there are approximately 4988 heating hours per year.  A 100hp compressor running 24/7 at an average of 80% load and paying $.90/Therm will yield a savings of $15,523 per year.

If the outdoor temperature is 40°F and you desire a plant temperature of 70°F, the EES system will deliver 6000 CFM of positive air flow to the facility.

The investment required for this option on a 100 HP is approximately $9,000.00.

Some frequently asked questions:

Q: Does this include the price of ductwork?
A: No, ductwork required to direct the heat either to the plant or outside is additional.  These are typically single runs with no tees or louvers, and normally are less than you would spend on installing ductwork with manual actuators.

Q: Can my local HVAC contractor do the same with louvers and ductwork?
A: Yes, but our experience is that it takes up much more space and is more expensive than the cost of the EES unit if you match controls apples to apples.

Q: Why don’t I manually switch the damper I  have added to the duct and save the expense of the EES?
A: Six months out of the year that might makes sense, but the other six months, fall and spring, you could be switching the damper numerous times per day, depending on the outside temperature.

Q: How does it know when my plant needs heat?
A: A remote thermostat is located in the plant, typically in the same general area as the discharge of the heat.  If you have it set to 70°F, and the plant is at 68°F, it will open the louver to direct heat into the facility.  As the temperature increases and approaches 70°F, the louver to outside will begin to open and the plant louver will close, directing the unwanted heat outside.

Q: Will this do any damage to my compressor?
A: No, there is a secondary thermostat inside the compressor cabinet that controls additional louvers that blend heat with the incoming cold air in winter to keep the compressor cabinet at a constant temperature preventing freezing.

Q: Can I buy the compressor now and add the EES later?
A: No, the package comes complete from the factory.

EES systems are available on air cooled compressors model 3000P (40hp) and larger.  It is a smart choice and typically has an ROI of less than 1 year overall.
 

Contact Information

Vice President (North Region): Steve Briscoe
Phone: 1-877-IACSERV X5006 
Email: sbriscoe@iacserv.com

Vice President (South Region): David Swinney
Phone: 1-877-IACSERV X1018
Email: dswinney@iacserv.com

About The Authors

Article written by: Joe Klawon and Steve Briscoe of Industrial Air Centers Inc.  Joe is the Area Manager for Industrial Air Centers, Inc. in Dayton, OH.  Steve is the North Region VP of Business Development for Industrial Air Centers, Inc.

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