In conducting energy audits of greenhouse operations, I have frequently observed uninsulated hot water system piping in areas where heat is not needed or where better control could be obtained if they were insulated.
It is surprising how much heat an uninsulated pipe gives off. One grower with two large boilers that heats a gutter-connected range told me that before insulating the supply/return pipes in his boiler room, he frequently had to leave the windows and doors open so that maintenance personnel could work in there. Once the pipes were insulated, they had to add extra heat to make it comfortable.
Heat loss from pipes depends on several factors including the diameter and length of the pipe, the water temperature inside the pipe, the air temperature surrounding the pipe, and the length of time that the pipe is carrying hot water. Adding insulation slows this loss and lowers the fuel bill.
Estimating your savings
Table 1 gives approximate annual savings from insulating a linear foot of different diameter pipe with 1 inch of fiberglass or foam. It assumes 2000 hours of annual use, typical of a heating system in a northern climate.
To use the table, select a pipe diameter and multiply the length of pipe by the savings from the table. For example, a grower can save $372 each year by insulating a 100 feet of 2 inch diameter heating system pipe carrying 180°F water if the boiler is fired with natural gas costing $1.05/therm. Savings = 100 feet x $3.72/linear foot = $372.
Table 1. Approximate annual fuel savings with pipe insulation (per linear foot)*
|Surface area (sq.ft)||Heat loss bare pipe
|1/2"||0.22 sq. ft.||52 Btu/hr-ft||11.5 Btu/hr-ft||$1.22||$2.83||$2.43|
* Assumes - steel pipe, 180F water temperature, 70F room air temperature, 2000 hours/year, 1" foam insulation, 70% heating system efficiency
Insulation material selection
Pipe insulating materials are selected based on where the pipes are located, maximum temperature of the water and the insulating value of the material. Most materials are available with formed pieces to fit over elbows and tees.
All pipe insulation materials are flexible or semi-rigid except for those that are enclosed in a protective jacket. This makes them easy to install in tight locations. Depending on the material, the length of individual pieces may be 2 – 6 feet. These can be cut with a utility knife to the desired length. All materials can either be slit to fit over an existing pipe or come in two pieces.
Due to the low service temperature, polyethylene materials are fine for use in domestic hot water systems but should not be used where the boiler water is greater than 200°F. All other materials can withstand higher temperature.
Table 2 gives the insulation factor for the different materials. The lower the "k" value, the better the insulation value and the greater the savings. Except for domestic hot water pipes that may contain 140°F water, all piping should have at least 1 inch thick insulation.
Installation time will depend on the material and access to put it on. Average time varies between 250 feet/day for the smaller sizes to 80 feet/day for the large sizes. Scaffolding or a man-lift may be required in some greenhouses. If a heating contractor installs the insulation, you can expect to pay labor costs of about $2.50 per linear foot for the small sizes to about $4 for the larger sizes. If done with your own labor during slack periods, it may cost considerably less.
Payback for most pipe instillation will be less than 2 years. USDA or state grant money may be available to offset some of the cost. See: www.dsireusa.org for information on grant programs.
Table 2 Pipe Insulation Selection
|UV polyethylene||200F||0.25||very low||outdoor/underground|
|Elastomer foam rubber||220||0.27||low||indoor|
*k - conductivity in Btu-in/hr-sq ft - F at 75F
John W. Bartok, Jr., Extension Professor Emeritus & Agricultural Engineer
Department of Natural Resources and the Environment University of Connecticut, Storrs, CT - 2015