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CBECC 2022: User & Standard Design for Res Mini DHWCentral Systems #143

Open joesinger12 opened 1 year ago

joesinger12 commented 1 year ago

Gather CEC and dev team to discuss limitations and simulation tweaks for situations where a residential central HPWH serves a small number of dwelling units. One user limit that is clear and should be implemented ASAP - a CheckCode preventing analysis when a res central HPWH system serves only 1 dwelling. User needs to define an individual dwelling DHW system in this case. Question of what the minimum (2+) number of served dwellings should be -plus- whether user and/or simulation inputs should be revised to more effectively describe and simulate mini-central/cluster systems. Consideration also needed for how standard design systems should be modeled for systems serving few dwelling units. This effort may identify a need for user input options to describe multiple res central HPWH systems (as opposed to the current limit of 1 per model).

SC: We got a support run w/ various problems - one of which results in the standard (ab) run throwing the following CSE error:

DHWLoopHeater 'dhwlphtr-MF0-CHPWH' of DHWSys 'dhwsys-MF0-CHPWH': HPWH message ((no date) hour 1 subHour 0): Resistance tank lower element wattage below 550 W. DOES NOT COMPUTE

The specific CSE input(s) causing this error are: whResHtPwr = 175 // Water heater resistance heat power (upper element watts), W whResHtPwr2 = 175 // Water heater resistance heat power (lower element watts), W which is set based on the standard design rule formula: 1.75 100 NumDwellingUnits CSE team is investigating lowering or eliminating this limit, but for the time being we should revise rules setting whResHtPwr* to ensure a value >= 550W.

Reported by: joesinger12

Original Ticket: cbecc-com/tickets/3477

joesinger12 commented 1 year ago

CEC/DT: For Q1, central system is defined as a water heating system that serves more than 1 dwelling. There are some projects that uses a single residential type HPWH to serve a small number of dwellings, some called these mini-central/cluster . I would say for central systems the number of dwelling serves must be >= 2. For the second part of the question, I think it is highly unlikely these mini-central systems would have a loop tank, or even a recir loop. I think we need a deeper dive to figure out how to set the standard design for the mini-central systems.

Original comment by: joesinger12

joesinger12 commented 1 year ago

CB: The 550 W limit is built into the HPWH resistance tank model. I think the rules re number of units should be formulated according to other considerations. Then however that works out, apply a minimum of 550 to the values passed to whResHtPwr and whResHtPwr2.

I could add a input-time check to CSE ... perhaps a warning plus change the value to 550 if a smaller value is supplied. Is that worth the effort?

Original comment by: joesinger12

joesinger12 commented 1 year ago

Diff:


--- old
+++ new
@@ -1,19 +1,14 @@
+Gather CEC and dev team to discuss limitations and simulation tweaks for situations where a residential central HPWH serves a small number of dwelling units.
+One user limit that is clear and should be implemented ASAP - a CheckCode preventing analysis when a res central HPWH system serves only 1 dwelling. User needs to define an individual dwelling DHW system in this case.
+Question of what the minimum (2+) number of served dwellings should be -plus- whether user and/or simulation inputs should be revised to more effectively describe and simulate mini-central/cluster systems. Consideration also needed for how standard design systems should be modeled for systems serving few dwelling units. This effort may identify a need for user input options to describe multiple res central HPWH systems (as opposed to the current limit of 1 per model).
+
 SC: We got a support run w/ various problems - one of which results in the standard (ab) run throwing the following CSE error:

 *DHWLoopHeater 'dhwlphtr-MF0-CHPWH' of DHWSys 'dhwsys-MF0-CHPWH': HPWH message ((no date) hour 1 subHour 0):
   Resistance tank lower element wattage below 550 W.  DOES NOT COMPUTE *

-The user input is clearly flawed - this is a small mixed-use building with a SINGLE 1-bedroom dwelling and they have assigned a central HPWH (commercial: AOSmith CAHP-120) as the DHW system.
-Q1) What is the minimum number of dwelling units we should allow for a central HPWH (or 'other' central system)?
-
-Is this even something we should control in the software?
-
-The proposed system runs fine but we then replace it with our standard central HPWH w/ a resistance loop heater (Series (Swing)) - and thats the simulation that throws this error. 
-The specific CSE input(s) that seem to be the issue here are:
+The specific CSE input(s) causing this error are:
       whResHtPwr = 175                  // Water heater resistance heat power (upper element watts), W
       whResHtPwr2 = 175                 // Water heater resistance heat power (lower element watts), W
 which is set based on the standard design rule formula:  1.75 * 100 * NumDwellingUnits
-
-Assuming this can never be < 550W (as the error message indicates), that would imply that the system needs to serve more than 3 dwellings or this limit will be triggered.
-
-If we want to allow for 2-3 dwellings to be served by a central HPWH should we revise this formula to be the minimum of 550 or the current calc - or should the CSE limit here be reduced - or should there be changes to if and how we setup standard design central HPWH systems to support small numbers of dwellings?
+CSE team is investigating lowering or eliminating this limit, but for the time being we should revise rules setting whResHtPwr* to ensure a value >= 550W.

Original comment by: joesinger12