Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
Sorry to be so late to this post, but I believe you'll find the details in this white paper found on the CBECC-Res Reference Documents page. In summary, a dataset of measured DHW draws from over 700 single-family homes in California were used to develop a set of discrete DHW draw events over the annual simulations. The draw events are defined by:
The "shuffle" or combination of DHW draw events used in the model depends on the number of bedrooms in the home (CBECC-Res) or apartment (CBECC-Com). This is all defined in the DHWDU.txt file that you mentioned (renamed to DHWDU2.txt recently), and is the approach used in both CBECC-Res and CBECC-Com. For CBECC-Com, there are multiple unique "shuffles" of DHW draw events for the same number of apartment bedrooms to capture the randomness of draws across the building. For example, a "1BR-A" set of draws is applied to a one-bed apartment and a different "1BR-B" set of draws is applied to a different one-bed apartment.
I'll note that this approach was applied to residential zones (apartments, common areas on residential floors, etc.) in multifamily projects of the new CBECC 2022. The non-residential zones (commercial retail, office, etc. typically on ground floor) in multifamily projects of CBECC 2022 CBECC-Com uses a simpler approach in EnergyPlus/OpenStudio (typical peak flow rate and hourly schedule for when draw events occur) instead of CSE because there is no data for non-residential draw patterns.
Below is an example of defining the annual "shuffle" of DHW draw events for a 1-BR home in CBECC-Res:
#define DHWSF1BR01 choose1(
$dayofyear,
"1H09",
"1D19",
"4E01",
...
Basically, for each day of the year, apply a different day of DHW draw events. The same for a 1-BR apartment in CBECC-Com would be named "DHWMF1BR01" (see lines 16-28 in DHWDU2.txt). For each daily draw name, letters signify the day type -- "H" for holiday, "D" for weekday, and "E" for weekend (see lines 37-40 in DHWDU2.txt).
Below is the DHW draw events for Jan 1 -- "1H09" -- defined with a DHWDAYUSE object:
DHWDAYUSE "1H09"
DWSH( 9.97, 1.500, 1.358, 0)
DWSH( 10.11, 1.000, 1.162, 0)
DWSH( 10.22, 1.333, 1.350, 0)
FAUC( 9.20, 0.262, 0.778, 0)
...
Each line is using a macro to set the type of draw (dishwasher for the first three, faucet for the fourth) and the other three DHW draw descriptors I mentioned at the top (when they start [hour of day], how long they last [minutes], what the average flow rate is over the draw event [gpm]). Here are the draw types (see lines 4786-4821 in DHWDU2.txt) that are defined with a DHWUSE object:
If you wanted to review outputs of hourly draw flow rates, you can add the following CSE lines to a text file and include that with your CBECC run (report include file defined in the Project tab):
REPORT "Fixture" rpType=DHWMTR rpDHWMeter=DHWMtrFXMix rpFreq=hour rpDayBeg=jan 1 rpDayEnd=dec 31 rpBtuSf=3412
REPORT "Heater" rpType=DHWMTR rpDHWMeter=DHWMtrWH rpFreq=hour rpDayBeg=jan 1 rpDayEnd=dec 31 rpBtuSf=3412
That will generate a .rep text file, so if you want a CSV output file instead replace "REPORT" with "EXPORT" and "rp###" with "ex###" for the inputs that follow.
