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5.3.6 Natural Ventilation - Specify or restrict supplementary HVAC systems to handle UMLH #195

Closed GoogleCodeExporter closed 9 years ago

GoogleCodeExporter commented 9 years ago 
What NACM Section(s) are relevant to this issue?

5.3.6 Natural Ventilation
5.7.5.3 Evaporative Cooler

Explanation of issue:

Jeff Stein comment: if the natural ventilation system can meet the loads and 
has excessive UMLH, put in a split DX unit with no economizer.

Proposed resolution:

For these systems, require the user to enter a "supplementary" system to meet 
the cooling loads.  Place restrictions on supplementary unit - efficiency 
cannot exceed Standards, no economizer. This will require a new building 
descriptor to distinguish "supplementary" systems from other types of systems.

Please provide any additional information below.

Original issue reported on code.google.com by JohnJArent on 11 Apr 2013 at 4:29

GoogleCodeExporter commented 9 years ago 
I agree that the default cooling system should be very code-minimum. Something 
like a PTHP or other minimally-compliant DX-based system, no economozer, as 
Jeff proposed. The SZVAV currently reflected in the rule seems like it might 
give too much credit for poorly modeled/designed natural ventilation designs.  
I recommend against the user being able to define the supplementary system 
unless they have one actually designed.  Also, I don't see why a new descriptor 
is needed, recommend all the rules be described in the nat vent section.        

BTW, is nat vent included in release 1?  I am assuming NO since it was not 
listed in the document, but don't see any reason why this couldn't be included 
soon after.

Original comment by da...@360-analytics.com on 11 Apr 2013 at 4:51

GoogleCodeExporter commented 9 years ago 
I recommended to John that we make the user add the supplemental system because 
they need to integrate it with whatever they are actually designing (NV or 
evap) and I didn't want the rules to have to try to do that.  Specifically, 
they will be responsible for setting up controls that determine when the 
supplemental system will operate and when loads can be met by the installed 
system.  

The rules then would need to check the ACM specified characteristics of the 
system, but these will be that the efficiency, for example, is exactly X, as 
opposed to our normal check that the efficiency is better than a mandatory 
minimum.  

We need a special flag to indicate that the system included in the user model 
will not actually be built and needs to be subject to these special checks.

Original comment by rhedr...@archenergy.com on 11 Apr 2013 at 5:07

GoogleCodeExporter commented 9 years ago 
What you describe in the first paragraph sounds like users would be providing a 
basic design, and therefore potentially credit, for something that doesn't 
actually exist.  For example, lets say the user decides the supplemental system 
is a chilled water coil because they have a ChW plant in their building; is 
that acceptable?  If a DX coil is integrated into a user's evap cooler, 
wouldn't the user's fan be under-powered to meet the additional static?  What 
if there is no evap cooler, purely naturally ventilated?  In my mind, the rules 
that are capable of adapting to a lot of different situations/user-defined 
supplemental systems will get quite complex.

To make the analysis/comparison more stable, and because EnergyPlus/the SDD 
readily allow it, I think a separate, rule-defined supplemental zonal system 
modeled along-side the user-defined system (likely to be a evap cooler, 
DOAS/heating-only, etc) is more appropriate.  PTAC and PTHP are good candidates 
for this, since they generally have low efficiencies, can easily be described 
and controlled independently, and there will be no incentive to have unmet 
loads met with them.  

Using this approach, one modeling rule is that the user can't already have a 
system type defined for the SDD "supplemental" system assignment...

Finally, there is currently no ruleset check to make sure the proposed minimum 
HVAC efficiency requirements are met; I think the only ruleset checking of 
mandatory requirements is of envelope performance.  Please let me know if this 
has changed.

Original comment by da...@360-analytics.com on 12 Apr 2013 at 9:20

GoogleCodeExporter commented 9 years ago 
I want the user to integrate a system where the characteristics are set by the 
ACM.  The user only would be setting things like availability schedules which 
would turn the supplemental system off when the installed system can meet the 
load.  I don't see how the rules could set this schedule.  

So basically I want to do what you are describing in your second paragraph, 
except the user is adding it to the model, and marking it as supplemental.  
Then the rules would check that it is a PTAC with EIR of X and no economizer, 
or whatever is specified.  If it doesn't meet the ACM requirements, the rules 
could change the efficiency or we could just kick it back again.  

In the boiler and chiller rules I am setting a check that the efficiency meets 
the mandatory requirements.

Original comment by rhedr...@archenergy.com on 12 Apr 2013 at 9:46

GoogleCodeExporter commented 9 years ago 
Perhaps we should discuss this at the next rule author meeting; I think we are 
close to being on the same page, but I think I am missing why it is important 
the user have control over specifying a system that does not exist.

John, can you confirm if it is a requirement that the rule software check 
meeting the mandatory minimum efficiencies?  I recall this explicitly being 
outside the scope of the tool (at least near-term).  There are a lot of 
categories on the air-side, and adding this will take some time, and I need to 
know how to prioritize...

Original comment by da...@360-analytics.com on 12 Apr 2013 at 10:04

GoogleCodeExporter commented 9 years ago 
I agree that checking mandatory requirements is not a priority right now.

Original comment by rhedr...@archenergy.com on 12 Apr 2013 at 10:36

GoogleCodeExporter commented 9 years ago 
I think the software should definitely check that mandatory minimum 
requirements as per Standards 110.2 are met.  Perhaps the ACM hasn't been clear 
enough about this requirement.

I have added some language for a "Supplementary DX Cooling Unit" attached. 
Basically it is a code-min-efficiency packaged DX unit (don't see any special 
reason to make it a split even though it might be in real life) with no 
economizer. Only proposed design capacity is specified by the user - the rest 
is hard-coded by the ACM/software.

Let me know how detailed this spec needs to be --- for example, I haven't 
specified min OA position, but I am assuming that it would be a fixed minimum 
required for ventilation (even if space is getting OA from natural vent and 
evap cooling).

I added some language in the natural vent section and evap cooling section to 
indicate when a Supplemental DX Cooling Unit must be specified.

Original comment by JohnJArent on 15 Apr 2013 at 9:43

Attachments:

GoogleCodeExporter commented 9 years ago 
I agree with everything you say except I think we need to allow the user to 
specify availability schedules or other controls to turn the supp. unit off 
when the evap or nat vent system can handle the load.  This is the reason I 
want the user to specify the system, we can't put in these controls through the 
rules.

Original comment by rhedr...@archenergy.com on 15 Apr 2013 at 9:51

GoogleCodeExporter commented 9 years ago 
John-
I did not find any language in the ACM that says the software checks to make 
sure proposed HVAC equipment meets Standard mandatory minimums; can you point 
me to where this is defined?  It is not a problem to set the proposed/baseline 
efficiency based on the requirements of a particular equipment category, as is 
proposed here, but to check proposed equipment efficiency values with respect 
to all categories in 110.2 and the appliance standards is a larger task; it was 
not planned for in Release 1 or versions that I had anticipated in the near 
future.  I agree it is a worthy feature of a compliance tool, and there has 
been discussion of including this in the scope of a separate, QC ruleset.  But 
based on your previous direction that mandatory requirements not addressed in 
the ACM should not be checked, we haven't focused on this.

Roger-
Is there no way to control the priority of separate AirLoop and ZoneHVAC 
systems to meet zone cooling loads?  That is, can you control ZoneHVAC systems 
to only turn ON if the AirLoop system cannot meet the load?  Better yet, do you 
have an example E+ file that describes how you would simulate natural 
ventilation in E+?  I think this would be helpful for NREL's translation 
efforts, as well as finalizing the ACM language.  

BTW, can we get final resolution on this question: NV is not included in 
Release 1, right?

Original comment by da...@360-analytics.com on 15 Apr 2013 at 10:27

GoogleCodeExporter commented 9 years ago 
There are ways to set priority on different systems.  I'm not sure how this 
could be used for natural ventilation though, as it is not modeled as a 
"system."  I am familiar with two ways to model nat vent.  One is to specify a 
natural ventilation object which allows airflow into a specific zone using an 
algorithm similar to that used for infiltration.  This has limits based on 
temperature conditions.  The other is to specify an airflow network.  This 
approach allows air to flow throughout the building based on pressure 
differentials and interzone openings.  Again, temperature controls can be 
applied.  Both of these approaches can control HVAC equipment as needed.  
However, I am not at all sure that we can identify a general approach to 
equipment control that will work with either.  

NV is not included in release 1.

Original comment by rhedr...@archenergy.com on 15 Apr 2013 at 11:39

GoogleCodeExporter commented 9 years ago 
Hi all-
Just wanted to follow-up on this, and summarize what Roger and I discussed in a 
call early last week:

I think we agreed that we will leverage the SDD's current specification of 3 
possible systems that can serve a zone:

Primary A/C (PrimAirCondgSysRef)
Ventilation (VentSysRef)
Secondary A/C (PrimAirCondgSysRef)

and let E+ to stage systems to meet the load. Also, to facilitate the use of 
ZoneHVAC systems, the system type installed by the ruleset into the proposed 
model should be a PTAC or PTHP.  Thinking about this more, I believe it should 
be a PTHP, since that way, no HW plant system needs to be added to the proposed 
design.

Here are a few examples or proposed user models:

1) Rooftop direct evap cooler has a fan to provide ventilation air and 
evap-cooled air.  Nat vent is used to supplement when conditions permit.  
Baseboard heaters are used to heat space.

VentSysRef -> AirSystem with evap cooler and fan -> AirLoopHVAC
PrimAirCondgSysRef -> ZoneSystem with baseboard coil, no fan -> 
ZoneHVAC:Baseboard
SecAirCondgSysRef -> SDD created, minimum code-compliant ZoneSystem (PTHP) -> 
ZoneHVAC:PackagedTerminalHeatPump
User specified PassiveCoolingMethod/Rate/Schedule

In this case, the combination of natural ventilation and the Vent/Prim systems 
are used to first meet the zone thermostat setpoints.  If and only if these 
systems can't meet the heating/cooling loads does the SecAirCondgSys kick-in to 
meet the load.

1) User provides no cooling/fan system; nat vent is used to meet both 
ventilation and cooling.  Baseboard heaters are used to heat space.

VentSysRef -> None
PrimAirCondgSysRef -> ZoneSystem with baseboard coil, no fan -> 
ZoneHVAC:Baseboard
SecAirCondgSysRef -> SDD created, minimum code-compliant ZoneSystem (PTHP) -> 
ZoneHVAC:PackagedTerminalHeatPump
User specified PassiveCoolingMethod/Rate/Schedule.  In this case, the vent rate 
needs to be at least the code-minimum requirement

Here the Prim system is heating only, and natural ventilation (untempered air) 
is used to meet the zone thermostat setpoints.  If user specified system/vent 
rate can't meet the heating/cooling loads, the SecAirCondgSys kicks-in to meet 
the load.

So, in conclusion:
If proposed design uses natural ventilation, the ruleset installs code-minimum 
compliant PTHP system into the user's design.  However, it is cycled on/off 
only if the Vent/Prim systems cannot meet the thermostat setpoint.

Feel free to outline other proposed configurations and we can see if the 
approach works.

Original comment by da...@360-analytics.com on 26 Apr 2013 at 5:59

GoogleCodeExporter commented 9 years ago 
Changing Priority status to High, since natural ventilation is now allowed in 
the Standard Design.

Original comment by JohnJArent on 4 Dec 2013 at 11:09

GoogleCodeExporter commented 9 years ago 
John, 
I think there is some confusion here between a) natural ventilation for meeting 
cooling loads, and b) natural ventilation for meeting outdoor air ventilation 
requirements.  I don't think the decision on how we treat natural ventilation 
in the context of outdoor air ventilation (issue #333) impacts the topic of 
this issue.  Basically, as I understand it, the rules and modeling of natural 
ventilation as a substitute for cooling is outside the current scope of CBECC.

Original comment by da...@360-analytics.com on 4 Dec 2013 at 11:23

GoogleCodeExporter commented 9 years ago 
Changing status to "Won't Fix", since this is outside the scope of CBECC (but 
not necessarily outside the scope of the ACM).

The intent here is to only allow modeling of natural ventilation for (a) 
meeting cooling loads when the ventilation source is controlled to maintain the 
space temperature at the thermostat.  

Similarly, natural ventilation for (b) ventilation purposes only shall only be 
allowed when there is means to ensure that ventilation is maintained during 
occupied hours. (No credit just for the presence of operable windows alone if 
they are manually operated.)

I will check to verify that this intent is clear in the ACM.

I think the use of ventilation with FPFC and PTAC systems should be verified -- 
I may open up a new issue to deal with this separately, since these systems 
normally do not provide outside air ventilation.

Original comment by JohnJArent on 18 Dec 2013 at 11:01