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joesinger12 / TestTicketTransfer

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DHW Modeling Enhancement #30

Open joesinger12 opened 7 years ago

joesinger12 commented 7 years ago

I am doing Performance envelope, lighting & water heating (not HVAC) modeling of a 5 story motel. There is only one water heating system for the entire building. The software keeps inserting another DHW system. Is this 2nd system merely a notation on the compliance form, or is the program actually modeling energy use for DHW 2 systems?

How do I get a correct report? Is there some “official” word from the CEC that this 2nd system is not real?

Reported by: joesinger12

Original Ticket: cbecc-com/tickets/1939

joesinger12 commented 7 years ago

Original comment by: joesinger12

joesinger12 commented 7 years ago

Not sure of what you are referring to as a second system. In CBECC-Com you build/define the DHW systems so unless you create a second system the program does not create one automatically. Please send us a model (cibd/cibdx/xml) and also are you using CBECC-Com or EnergyPro for your modeling?

Original comment by: joesinger12

joesinger12 commented 7 years ago

If you are using EnergyPro, EnergyPro maybe adding this additional water heater to account for pumping power in cases where you have a mix of residential and non-residential occupancies. You might want to check with EnergyPro support to confirm this.

Original comment by: joesinger12

joesinger12 commented 7 years ago

Original comment by: joesinger12

joesinger12 commented 7 years ago

User - I do have mixed residential & non-residential occupancies. All hotel/motels have mixed occupancies! There is however, only one system with only one recirculation pump. EnergyPro has already told me it is a CBECC-Com problem, see below.

“The pipe info is not used in the calc The two boiler issue is a limitation of CBECC it requires a separate boiler for res and nonres spaces in the simulation

Original comment by: joesinger12

joesinger12 commented 7 years ago

Yes we do model residential and non-residential separately in CBECC-Com. This is something that we will most likely be looking into in the next round of development. For now you will just need to add the explanation to the narrative section to clarify for the plan checker that the DHW is split into two systems due to software limitation.

Original comment by: joesinger12

joesinger12 commented 7 years ago

Original comment by: joesinger12

joesinger12 commented 7 years ago

9/2 CEC - Per our conversation, I wanted to elaborate on the DHW issue in CBECC-COM for work to be done in the future version.

For HRR buildings, sometimes the main residential central DHW system is also used to provide SHW to the nonresidential spaces (i.e. run a smaller hot-water pipe into the nonresidential spaces). But in order to model this, the user would have to enter in a Service Water Heating system, which would be identical to the central residential system, resulting in an oversized system for the nonresidential spaces and leads to probably inaccurate DHW calculations for the nonresidential spaces. Plus this results in weird reporting because the PRF-01 would show both systems, even though there is really only one in the project.

So I was thinking about redoing the way CBECC-Com would handle this. A thought I had was to add a checkbox or pulldown or something else to the Space Data tab to let the user indicate that the SHW for the nonresidential spaces would be coming from the residential DHW system.

Maybe add a new line item to the SHW FluidSeg pulldown saying something like “Use Residential DHW System”, then they would select the DHW system from the Res DHW Sys pulldown.

Then CBECC would create an ‘invisible’ SHW system and send that into E+ to get the nonres SHW energy usage and combine that with the CSE DHW usage. And CBECC would not report that ‘invisible’ SHW system on the PRF-01, so only the ONE DHW system (the res DHW) would be reported.

But if the nonres spaces had their own SHW system as part of the design, then the user would model them just as they would now (the Res would use the Res central system and the nonres would use their own SHW systems).

I was trying to noodle through how the ‘invisible’ nonresidential baseline and proposed SHW systems should be modeled. I think the ‘fairest’ way would be to have the baseline system be what it used to be (use the hot-water loads from the table to determine the water usage and do the 60/40 split as described in the ACM). And maybe the ‘invisible’ proposed system would just be a scaled down version of the proposed res central system..scaled down so the hot-water use matches what was calculated for the ‘invisible’ basleine system.

An example would be the scenario we discussed, where the user had a 3M BTUH boiler (say 95% efficient) with a 600 gallon storage tank. This would convert to a large instantaneous system. So the total rated hot-water capacity would be (3,000,000 0.95)/(8.33 80) + (600) = 4,876 first-hour-gallons of hot water (which may be perfectly fine for the entire building once it’s completely modeled). And say the nonres space (5,000 ft2 retail) only needed 15 first-hour-gallons (83.3 occ * 0.18 GPH). So the ‘invisible’ proposed SHW system would be scaled down by 0.3% (15 / 4,876) resulting in an instantaneous system with 9,000 BTUH input (at 95% efficient) with a 1.8 gallon storage tank. And the baseline SHW would be per the ACM (I’m making up a system with an input of 7,500 BTUH with a 6 gallon tank, or something close to that).

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joesinger12 commented 7 years ago

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