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).
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
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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 ---------------------------------------------------------