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Residential DHW Flow Rates in CA Software

asked 2020-11-26 13:54:40 -0500

updated 2022-12-18 19:01:39 -0500

I know that CBECC-Com and CBECC-Res both use the CSE engine's DHW system calculations for residential space types. I am trying to figure out how the calculation works for multi-family projects, so I can better compare these assumptions to those in the design.

Ideally, I'd like to understand the calculations so I can replicate the peak demand flow rate and hourly (sub-hourly?) schedules. I would settle for being able to extract this info from a T24 compliance simulation after running in CBECC-Com.

I have read Appendix B in the Residential ACM, "Water Heating Calculation Method". It seems to explain how the calculation works, but I just can't make sense of it. I've also reviewed the relevant publications referenced in Appendix F.

I have scoured the files and subdirectories after running a CBECC-Com simulation. I haven't found any files that show the relevant input or results info to/from the CSE engine to give me what I want.

The DHWDU.txt looks to include the hot water draw profiles used for single and multi-family dwelling units, but I haven't been able to reverse-engineer the profiles to make sense of them.

Does somebody out there have a reference you can share or an explanation for building up draw profiles from the DHWDU.txt file? Thanks in advance.

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Hi Greg - I don't know much about CSE, but maybe the GitHub repo has what you're looking for...

MatthewSteen's avatar MatthewSteen  ( 2020-11-27 14:21:39 -0500 )edit

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answered 2022-12-23 17:03:32 -0500

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:

  • when they start
  • how long they last
  • what the average flow rate is over the draw event
  • what DHW draw type it is (shower, sink, clothes washer, etc.)

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(

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:

  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:

  • SHWR: shower
  • CWSH: clothes washer
  • FAUC: faucet
  • BATH: bath
  • DWSH: dishwasher

If you wanted to review outputs of hourly draw flow ... (more)

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Thanks for this detailed explanation Aaron!

ericmartinpe's avatar ericmartinpe  ( 2022-12-27 18:39:36 -0500 )edit

Aaron, this is the best explanation of DHW in CBECC that I've seen, thank you!

Nick Brown's avatar Nick Brown  ( 2023-06-08 13:29:46 -0500 )edit

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Asked: 2020-11-26 13:54:40 -0500

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Last updated: Jun 08 '23