Pre-flighting and climbing into a warm airplane in the dead of winter is a luxury that many hangar owners and renters can only dream about. However, a heated hangar is essential for service center providers, aircraft management companies, and FBOs as their operation would be impossible without it. Regardless of who you are, the cost of keeping your hangar warm 24/7 or just a few days at a time is a cost that must always be in the forethought of your mind.
Hangars are unique structures to heat as they possess a feature that permits massive temperature swings in just moments: the hangar door. If you own or manage a commercial hangar with frequent door “events,” chances are you cringe every time you open your door and witness the warping of light when warm and cold air collide, a physical representation of cash flying out the door.
HangarSphere sought out the technical expertise of Jim Melcher of Cambridge Engineering Inc. in Chesterfield, MO. I asked him to develope a simple equation that would help assign a quantitative, financial cost related to replenishing the heat lost when a hangar door is opened during the winter months.
The variables affecting thermal dynamics are many which is why we are taking on a simplistic approach to the equation. The equation focuses strictly on the energy required to raise a specific volume of air a given number of degrees Fahrenheit yielding a “ball park” answer. It represents a “worst” case scenario as it assumes total heat loss to the outside with no regards for insulation, drafts, residual heat, humidity, etc. Finally, it also assumes a 100% efficiency rating for a gas fired unit where “real world” units range from 80 to 92%.
Defining The Terms
Volume of Air – This number represents your hangar’s total number of cubic feet of air and is derived by multiplying the length times width times height of the building.
Volume = Length x Width x Height
∆T – ∆ represents “change” and T represents “Temperature.” Together, it represents the “change in temperature” or the desired rise in temperature. In the example below, ∆T is 50 degrees Fahrenheit assuming the outdoor temperature is 0 degrees and the target hangar temperature is 50 degrees.
Heat Transfer Factor – This is the specific heat of dry air (0.24 Btu/ lb/°F) x (inlet air density – lb/ft³) x 60 min./hr. For our purposes, we will use the factor of 1.08.
BTU – The British Thermal Unit is a measure of energy. One BTU is required to raise the temperature of one pound of water one degree Fahrenheit.
Therm – One Therm is equal to 100,000 BTUs. When you review your natural gas bill, you will observe that you are charged by the number of Therms you consumed. Rates per Therm vary across the country.
- Hangar Volume = 250,000 Cubic Feet (100′ x 100′ x 25′)
- Desired hangar temperature: 50 degrees F
- Outdoor air temperature: 0 degrees F
- Furnace Rating: Based on 100% efficiency (real world ranges from 80-92%, factor in your efficiency rating for greater accuracy)
- Assume total heat loss of indoor air when hangar door is opened
- Cost per Therm = $.999 (U.S. National Average For Month of November 2013. Source: U.S. Bureau of Labor Statistics
- The highlighted figures are ones dependent upon the size of your hangar, the cost per Therm per your local utility, and your furnace’s efficiency rating.
- Cost to reheat sample hangar from 0 degrees to 50 degrees Fahrenheit after opening your hangar door = $134.87.
Items to consider when owning or managing a hangar with heat is the frequency of door opening events. Make every attempt to group aircraft movements in and out of the hangar at one single time. Be as quick and as safe as possible with aircraft movements and have someone engage the door as soon as aircraft are clear. These simple techniques could save hundreds or even thousands per month in heating costs and make a real difference for tight budgets.
About Cambridge Engineering Inc.
Since 1963, Cambridge Engineering has been the Performance Leader in Industrial Space Heating and Make-Up Air. Being the best at saving energy, reducing operating costs and improving indoor air quality has made Cambridge technologies very popular with 30,000 installations and over one billion square feet heated. You can reach Cambridge Engineering Inc. by phone at 800-899-1989 or on the web at http://www.cambridge-eng.com.