Sizing electric tankless Domestic Hot Water system
Sizing electric tankless Domestic Hot Water system
(OP)
Hello,
I wanted to inquire if an electric tankless domestic hot water system could be sized per apartment square footage?
I'm looking to size a tankless DHW system for a 900 sqft apartment with one bedroom and den. The plumbing fixtures which require hot water are the kitchen faucet, washroom faucet, bathtub (which also has a shower head), clothes washer, and dishwasher.
Is there a rule of thumb which I could use to size a tankless system or do I require information such as fixture GPM, minimum inlet water temperature (42 degree fehrenheit), temperature rise (140 minus 42 = 98 degree fehrenheit)? Also what would information on a spec sheet such as Temp rise @ 1.5GPM - 98 F, @ 4GPM - 49 F, @ 6GPM - 33 F mean? Do I still have to meet a temperature rise of 98 F for any flow rate?
I'd appreciate your comments (preferably with a basic example if possible) to help me size tankless domestic hot water systems.
Thank you.
I wanted to inquire if an electric tankless domestic hot water system could be sized per apartment square footage?
I'm looking to size a tankless DHW system for a 900 sqft apartment with one bedroom and den. The plumbing fixtures which require hot water are the kitchen faucet, washroom faucet, bathtub (which also has a shower head), clothes washer, and dishwasher.
Is there a rule of thumb which I could use to size a tankless system or do I require information such as fixture GPM, minimum inlet water temperature (42 degree fehrenheit), temperature rise (140 minus 42 = 98 degree fehrenheit)? Also what would information on a spec sheet such as Temp rise @ 1.5GPM - 98 F, @ 4GPM - 49 F, @ 6GPM - 33 F mean? Do I still have to meet a temperature rise of 98 F for any flow rate?
I'd appreciate your comments (preferably with a basic example if possible) to help me size tankless domestic hot water systems.
Thank you.





RE: Sizing electric tankless Domestic Hot Water system
Perhaps you need to do an audit or survey as suggested by http://www.rheem.com/products/tank_water_heaters/h...
see also:
http://learn.compactappliance.com/tankless-water-h...
http://www.homedepot.com/c/water_heater_buying_gui...
http://energy.gov/energysaver/sizing-new-water-hea...
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RE: Sizing electric tankless Domestic Hot Water system
The instantaneous water heater manufacturers will have tables which indicate the temperature rise at different flow rates for their equipment.
Your washing faucet is likely to be the culprit. Typical rule of thumb is 5 gpm (although they can go as high as 10 gpm). This has nothing to do with water efficient washers, which reduce the total volume of water used, but not the flow rate into the equipment. However, you will not find an instantaneous water heater that will give you the temperature rise at this flow rate. A lot of the heaters have a flow restrictor which helps this. More than likely, your maximum flow will be 2.0-2.5 gpm.
You are likely looking at a 20 KW version with 96 Amps to get hot enough water.
RE: Sizing electric tankless Domestic Hot Water system
My instant electric shower runs at about 8-10litres/min and is rated at 9kW. I personally would not want it to fill a bath at that rate as it would take a seriously long time.
Hence my guess is you're looking at a 15 to 20kW heater (!!)
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RE: Sizing electric tankless Domestic Hot Water system
RE: Sizing electric tankless Domestic Hot Water system
It does help me figure out the required size by doing the calculations and selecting the correct size by reviewing the manufacturer's spec sheet.
RE: Sizing electric tankless Domestic Hot Water system