By Jeff Crane, P.E., LEED® AP
Published in the December 2005 issue of Today’s Facility Manager
With higher prices for natural gas and other energy commodities this winter, facilities managers in all sectors are revisiting efficiency projects and making sure they’re getting the most value from every BTU consumed. If a facility manager is new to the industry or he or she wants to interpret this article for a boss who doesn’t understand non-currency conversations, BTU stands for British Thermal Unit—a common term associated with energy measurement. Specifically, a BTU is the amount of heat required to raise the temperature of one pound of water exactly 1°F at sea level
Typically, industrial facilities with energy intensive production lines react quickly to energy price increases. Hospitals, schools, office buildings, and retail facilities sometimes take longer to realize that an energy strategy (or lack of one) can impact profitability. In crafting or updating an energy strategy, a facility manager should recognize that efficiency projects where ROI (return on investment) wasn’t attractive yesterday might make more sense today.
As we hunt for energy efficiency opportunities, the obvious goal is to reduce dollars spent. But since we trade dollars for utilities each month, the real goal is to track, capture, and eliminate unnecessary BTUs. How do we do this? Like all engineers, doctors, attorneys, and consultants, I can share some general suggestions without knowing the specifics of the situation.
Let’s begin our quest for big game with boiler operations. For boilers connected to sensitive equipment or processes, it’s always best to engage a licensed mechanical engineer to conduct load calculations and evaluate equipment capabilities before making adjustments. However, facility managers with steam or hot water boilers for comfort or process heating can immediately declare hunting season on the elusive BTU.
• Operating Pressure: Boilers are typically run at a specific operating pressure for the worst possible reason: “Because it has always been done that way.” A boiler’s optimum pressure depends on several factors including the pressure drop throughout the system, condensate return, and the highest steam pressure required at any point. Lowering boiler operating pressures reduces the energy required to heat water and make steam. Like most engineered systems, boilers are commonly sized to handle the maximum load anticipated when designed. As a result, they’re usually capable of producing much more steam than we need. Our goal is to run boilers at the lowest possible operating pressure while satisfying the load.
Potential Project: This might sound silly, but one simple way to determine optimum boiler pressure is to drop the operating pressure one psi each day until someone complains. Pressure drops of five, 10, or more than 20 psi might be possible before anyone notices a change in system performance and begins to complain. Calculating fuel (and dollar) savings is relatively simple and would be a great attachment for any facility manager’s performance review.
This potential project is relatively safe for comfort heating applications, although boiler manufacturers’ operations manuals should always be consulted for operating pressure guidance.
• Condensate Return: One of the most valuable things in a facility (after the facility manager’s staff, of course) is the pure, hot condensate returned to the boilers. As steam condenses in heat exchangers and process equipment, condensate (sometimes well above 200°F) can be returned to the boilers with some combination of gravity, traps, pressure, and pumps. An effective condensate recovery strategy reduces the amount of water and chemicals needed to feed the boiler, but, more importantly, it recycles enormous amounts of energy and reduces the burner fuel required to make more steam.
Potential Project: Facilities with steam boilers typically engage a water treatment contractor for applying chemicals to prevent problems in the boiler, steam, and condensate lines. As part of its periodic service, the water treatment contractor can help trace system lines and calculate the percentage of condensate returning to the boiler. Although it’s impossible to return 100% of the condensate, it’s important to understand where steam is being used and how much energy might be recoverable. The water treatment contractor can also explain the water treatment strategy (including softeners or chemical pre-treatments) and confirm the boiler is operating at safe, but efficient, conductivity levels or cycles of concentration.
In many steam applications (particularly comfort heating), condensate return presents a fantastic energy recovery opportunity. However, when steam is directly consumed in a production process, used as a product ingredient, or becomes contaminated during its use, there may not be any condensate returned to the boilers. If boiler treatment options are approached with non-chemical, alternative options, we should be very skeptical and do a lot of homework before abandoning conventional programs (see note above about chemical costs relative to burner fuel. Also, the cost and inconvenience of replacing or acid cleaning an old or fouled boiler is tremendous).
Like many systems in our facilities, boilers are complex and consume enormous amounts of energy. Whether heating and humidifying a conference room in an air handler or melting asphalt in a pipeline steam jacket, the challenge is to get the most value from the BTUs we purchase.
Good luck with your hunting this winter!
Cranei s a mechanical engineer and regional property manager with Childress Klein Properties, a leading real estate developer and property management services provider in the Southeast.