[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
RE: [EnergyPlus_Support] Re: HSPF in various climate zones
I have (naively, it appears) assumed that HSPF for energy models was a stable value, independent of modeling assumptions. Not so! Climate zone makes a very big impact and ASHRAE 90.1 does not appear to specify "HSPF for Climate Zone IV". In addition, the outdoor temperature values for energizing / de-energizing the heat pump ar not specified and make a big difference.
It seems that, depending on the project climate, on/off temperatures and performance curve assumptions, HSPF can mean completely different things regarding efficiency. That is OK for AHRI's purposes, but I suspect it's not what ASHRAE intended.
The Building Performance Team
James V. Dirkes II, P.E., BEMP , LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653
________________________________________
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Chip Barnaby [cbarnaby@xxxxxxxxxxxxxx]
Sent: Monday, September 23, 2013 10:44
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Re: HSPF in various climate zones
Jim,
I believe the HSPF value specified for the baseline is the Climate Region IV HSPF as defined in AHRI 210/240 and various precursor standards. Thus, this is a single rating for any (US) heat pump, no matter where you live. That defines what should be run in the baseline.
However, there is a *major* problem that there are many ways to build a heat pump having a given calculated HSPF. Those variants will not have the same performance in different climates even though they have the same rated HSPF. Various models have various schemes for defaulting the pertinent parameters (and curves) from HSPF, so you won't necessarily get the same baseline performance for the same HSPF when using different programs (all else being equal).
Further compounding the situation is that AHRI test conditions can yield ratings for operating conditions that never occur in the field. For example, for a variable speed unit, the 47 F full speed rating point is measured at full compressor speed (not surprisingly), however in many cases, in actual operation, controls limit the compressor speed. The rated HSPF uses the 47 F point, so then HSPF embodies performance that never happens in the field.
All-in-all, the energy performance simulation use case is very poorly supported by the data definitions used for ratings and product descriptions. This is true for many types of equipment but particularly for air source heat pumps. The models in EnergyPlus etc. attempt to do a plausible job via back-guesstimating the characteristics based on the ratings, but given that in at least some cases the rating points don't correspond to actual operation, there are real limits on what can be done.
ASHRAE Standard 205P is addressing this issue ("Standard Representation of Performance Simulation Data for HVAC&R and Other Facility Equipment") by specifying common data definitions and formats for the info our domain needs for rigorous modeling of equipment performance. I encourage people in the modeling community to get involved in development of Standard 205 (eMail me for more info).
Chip Barnaby
Wrightsoft
===============================
Sun Sep 22, 2013 10:29 am (PDT) . Posted by:
"Jim Dirkes" jvd2pe <mailto:jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx?subject=Re%3A%20HSPF%20in%20various%20climate%20zones>
Dear modeling communities,
We're busy trying to reach ASHRAE 90.1-specified HSPF values for a project that requires heat pumps in the baseline energy model and have constructed the calculation procedure in Excel (at least we think we have!)
It appears to be the case that reaching a specific HSPF value is dramatically more difficult in climate Zone V (where I live) than in Climate Zone II - due to heat pumps performing better in warmer climate regions.
Nonetheless, ASHRAE 90.1 makes no distinction for the required HSPF by climate zone
I'm not even sure that a heat pump is commercially available with HSPF of 7.7 for Climate Zone V! Have any of you investigated this? Have you found this to be true? Have you modeled HSPF for climate zone V and seen favorable savings for alternative systems?
The Building Performance Team
James V. Dirkes II, P.E., BEMP , LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653
---------------------------------------------------------
Chip Barnaby, BEMP cbarnaby@xxxxxxxxxxxxxx
Vice President of Research
Wrightsoft Corp. 781-862-8719 x118 voice
131 Hartwell Ave 781-861-2058 fax
Lexington, MA 02421 www.wrightsoft.com
<http://www.wrightsoft.com/>---------------------------------------------------------
------------------------------------
Primary EnergyPlus support is found at:
http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx
The primary EnergyPlus web site is found at:
http://www.energyplus.gov
The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/
Attachments are currently allowed but be mindful that not everyone has a high speed connection. Limit attachments to small files.
EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/EnergyPlus_Support/
<*> Your email settings:
Individual Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/EnergyPlus_Support/join
(Yahoo! ID required)
<*> To change settings via email:
EnergyPlus_Support-digest@xxxxxxxxxxxxxxx
EnergyPlus_Support-fullfeatured@xxxxxxxxxxxxxxx
<*> To unsubscribe from this group, send an email to:
EnergyPlus_Support-unsubscribe@xxxxxxxxxxxxxxx
<*> Your use of Yahoo! Groups is subject to:
http://info.yahoo.com/legal/us/yahoo/utos/terms/