I am on a solar decathlon team, and we are trying to size our pumps for supplying water to the house. In order to do this, we need to know the maximum demand required from all appliances.

We are having trouble locating the flow rates for our washing machine and dishwasher. Do you know the incoming water flow rate for the LG WM1355H, GE WCVH4800KW, Frigidaire FAFW4011L or the Frigidaire FAFS4473L washing machine? Also, the dishwashers have not been narrowed yet, so do you know of an estimate flow rate for the average Energy Star dishwasher?

Answer from Green Energy Efficient Homes

I’m afraid I don’t have access to the flow rates for these specific appliances – other than what can be found in the owner’s manuals. For example for the LG WM1355H washer, the water supply pressure must be between 14.5 PSI and 116 PSI (100~800 kPa); for the FAFW4011, water pressure should be between 30 and 120 PSI, with no more than a 10 PSI difference between hot and cold; and for the FAFS4473L you’ll need water pressure of at least 30 PSI.

However, I don’t think you can convert between pressure and flow – since you could have very high pressure in a thin pipe, but the thinness of the pipe would prevent flow from exceeding a certain rate, while you could have very low pressure in a very thick pipe, and still get a very high rate of flow.

In general though, you need about 3 GPM (gallons per minute) or 11 L/m (liters / minute) of flow for both washing machines and dishwashers.

For solar hot water heating, you can of course meet the demand of any number of appliances by installing enough pump capacity, but I think this would be overkill (although that doesn’t mean it’s not required by local building codes). Most of my neighbors are careful not to start the dishwasher and washing machine at the same time, and most try not to take a shower while either is running. Of course we live on a street with pretty low water pressure, in 90-year-old houses with 3/8″ piping that is probably half-clogged with scale!

Sorry I can’t be of more help, but best of luck with your solar decathlon project. If you’d like to add a comment to this page explaining what it is, that would be much appreciated.

1 reply
  1. Dave
    Dave says:

    The best default for good operation on any household appliance would be between 20psi and 80psi. If the LG washer says it will operate on 120psi , it would, but that puts your hot water tank or any other storage tank at risk and your home plumbing system at a dangerous level for children or the elderly. The flow to home appliances and plumbing should not be the consideration; as long as you base your system on the common 1/2 inch pipe at 20psi to 80psi. All things being equal the flow will always be adequate because it is a constant as long as pressure and size remain constant. Clothes washers, dish washers and ice makers all use pressure sensitive electric fill valves. It is very important to keep your pressure between the 20-80psi for proper operation. Many of these valves use the water pressure to close the valve; if too low, you could have a run away open valve.

    If you are looking for an ideal pressure I think 40 to 50psi gives the best operation of your appliances. If you are at 20psi and you get a dirty filter screen to the input valve you could have a 10psi or less condition. Having the extra 20lbs of pressure allows for deviations. Codes usually call for a 1 inch or 3/4 inch main water pipe to an average dwelling. Then 1/2 inch pipe throughout the dwelling. Remember the key here is the ability to maintain the desired pressure regardless of the draw; this is where the flow is critical and again why the 40 to 50psi gives you the leeway if minor problems occur.

    Hope this made sense.

    Dave

    Reply

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