Performance requirements for Water Heating Equipment
I am trying to calculate Water Heating Equipment, it looks like that I should have the EF, Et and SL as per description below the table 7.8 of 90.1 2007. For the base case where can I get these numbers from? I looked in reference guide as well could not find a clue.
"Energy factor (EF) and thermal efficiency (Et) are minimum requirements, while standby loss (SL) is maximum Btu/h based on a 70°F temperature difference between stored water and ambient requirements. In the EF equation, V is the rated volume in gallons. In the SL equation, V is the rated volume in gallons and Q is the nameplate input rate in Btu/h."
I am using TAS so I just need to enter total hot water energy requirement (kWh) which I have and system efficiency.
Thanks in Advance
Christopher Schaffner
CEO & FounderThe Green Engineer
LEEDuser Expert
962 thumbs up
June 21, 2010 - 9:39 am
Not sure I completely understand the question.
For your base case, all those numbers should be the ones in Table 7.8. For the design case, the manufacturer should provide the numbers.
V. Miller
WSP78 thumbs up
June 22, 2010 - 1:37 am
Thanks Chris,
Ok as you say the base case should use the numbers in the table. Say for Electric water heaters >12kW, table says Performance required is "20+35 √V SL, Btu/h". V is the volume and SL is “stand by loss”. How can I get the SL figure?
Secondly is the “Performance Required” equal to COP?
Assuming there is no SL then the overalls result would be 20? 20 can not be a water heater COP? Normally we are talking about COP of 85% to 95% for electric water heaters.
Would you please enlighten me?
Cheers,
Christopher Schaffner
CEO & FounderThe Green Engineer
LEEDuser Expert
962 thumbs up
June 25, 2010 - 3:19 pm
I think you've misinterpreted the formula.
20+35*√V=SL in BTU/H.
So for a 25 gallon tank (let's say), the maximum Standby Loss (SL) is:
20+35 *√25=20+35*5=195 btu/hr
V. Miller
WSP78 thumbs up
June 27, 2010 - 1:25 am
Thanks Chris, this was very useful.
3 thumbs up
December 1, 2022 - 12:21 pm
Hi Chris, Could you do an example for a 50 gallon gas water heater with 76,000 Btu/hr input? Is the Et term for baseline and proposed supposed to be prescriptive and design values, respectively?
EDIT: I found an example in the 90.1-2013 User's Manual. :-)