Day Tank Size

Q.  Do you have a suggested minimum size for a hospital day tank? I know about the maximum size, but had not heard of a minimum.

A. Minimum size depends on the GPH of fuel burned at full load, whether the “return line” goes to the daytank or main tank, and whether there is a “fuel cooler” in place.  There are no minimum “standards” per se in any NFPA document I am aware of.

If there is no fuel cooler (normally mounted in front of the radiator) and the return line goes to the daytank, I like to use, at a minimum, 2 times the max GPH the engine would burn, which is about .08 x kw of load.  (E.G., 1000 kW x .08 = 80 GPH x 2 = 160 gallons).  Some engines get better “gas mileage” than others (I have seen .067 per kW measured on a new CAT), which could reduce the design/size of the daytank.

If there is a fuel cooler, and/or the return line goes back to the main tank, you can get away with something much smaller.

The key is keeping the fuel in the supply line below the maximum temperature as recommended by the engine manufacturer.  Remember, a diesel returns a great deal more fuel (hot) to the tank than it burns.  When diesel fuel gets hot, it expands…therefore reducing horsepower (and kW), because of the way injectors are metered..

Dan Chisholm