By DENNIS BUFFINGTON
Contributing writer
A dairy accounting firm reported for 2010 that energy expenses (utilities and fuel and oil combined) cost an average of $138 per cow per year. The category of energy expenses was reported as the eighth largest production cost on dairies and was one of the fastest increasing.
Modern dairies today depend upon significant amounts of energy in various forms. Heating water is often cited as the most energy-intensive function on the dairy farm.
Systems
Today there are many types of water heating systems available that can use a variety of energy sources. The more common types of water heating systems include:
Storage tank water heaters; tankless “on-demand” water heaters; heat pump water heaters; hybrid heat pump water heaters; hot-water supply boilers; combinations of those listed.
Water heaters utilize various forms of energy including electricity, natural gas, LP gas, propane, fuel oil, and solid fuels such as coal and biomass (chunk wood, wood chips, biomass pellets, and crop residues).
In addition, solar energy is being utilized as an energy source. The most appropriate energy source to use for heating water depends on the type of water heating system and the delivered prices for energy to your farm.
Propane, LP gas, natural gas, fuel oil, and electricity are the usual energy sources for the storage tank and tankless water heaters. Nearly all heat pump water heaters use electricity as the energy source.
The solid fuels can only be used with the hot-water supply boilers. Given its fluctuating nature, solar energy can only be relied upon for pre-heating water for the dairy farm.
Recovered energy
Another energy source for heating water is energy recovered from a variety of on-farm sources including reject heat from refrigeration condensers, plate coolers and vacuum pumps. The systems installed to recover the refrigerant heat from condensers are called desuperheaters.
With these energy recovery systems, water is heated only when the host equipment components are operating; therefore, these recovery systems can never be relied upon to provide all the energy needed for heating water for dairy farms.
Like solar energy, the energy from recovery systems should only be used for pre-heating water before it enters the water heaters.
Comparing
However, it needs to be emphasized that not all models of tankless water heaters can be used to heat water that has already been pre-heated. The only way to compare the cost of one energy source compared to another is on the basis of dollars per million BTUs.
You can download an Excel spreadsheet at http://energy.cas.psu.edu/costcomparator.html that will enable you to make quick and easy cost comparisons of the various energy sources.
However, recovered energy and solar energy cannot be evaluated with this spreadsheet; for these energy sources, you need to calculate the costs for installation and operation to make comparisons.
Factors
There is no one type of water heater that can be recommended because of the differing characteristics of each dairy farm. Each farm has its unique requirements for both the quantity of hot water needed and the required temperature(s) of the hot water.
However, there is one generalization that can be made concerning water heaters on dairy farms. Unless you have a very small dairy farm with no milking pipeline system, then you must choose a commercial or industrial water heating system as opposed to a residential water heater.
A residential water heater does not have the design features to produce the volume of water at the required high temperatures to operate in an efficient, cost-effective manner on a modern dairy farm.
(By Dennis Buffington, professor, Penn State Department of Agricultural and Biological Engineering.)
