ASHRAE Journal - April 2020 - 56

ASHRAE - CELEBRATING 125 YEARS

smaller/lighter with lower sound,
and oil/friction free.

FIGURE 3 Sound level and associated issue comparison.

The Bet
This was not a low-cost solution. That ﬁrst ~90 ton/300
kW compressor was created on a bet that the mid-capacity HVAC market would pay a premium for a compressor
that was:
* ~30% to 50% more efﬁcient than it's constant-speed
competitors
* ~25% of the physical footprint of the positive displacement competition
* ~8dBA lower sound than the positive displacement
competition
* Simpliﬁed the system design and eliminated
long-term performance degradation resulting from
56

ASHRAE JOURNAL

ashrae.org

APRI L 2020

Inherently Quiet, With
No Expensive Sound
Attenuation Required

No Annoying Tonal Sound
Issues

FIGURE 4 Regional variations in air-cooled chiller ambient rating conditions/
weighting factor.

IMAGE: DANFOSS

Around the time that this com~8 dBA Quieter vs.
pressor was ﬁrst commercializing,
Comparable Size Screw
the industry was also coming to the
Compressor
realization that part load efﬁciency
was critical, with ASHRAE 90.1 equipment efﬁciency ratings changing to reﬂect the ~1% of the time that an average chiller operates fully loaded. The compressor technology choices and resulting oil-free operation enabled
several beneﬁts, most of which relate to part load efﬁciency and/or increased efﬁciency at higher differential
temperatures (pressure ratios):
* Compressor turndown-Turndown with previous
compression technologies was signiﬁcantly limited by
the differential temperature and resulting pressure
required to move oil through the system.
* Variable/high-speed-Variable speed in combination with high-speed operation enable highly-efﬁcient
operation, speciﬁcally around the 75% and 50% load
points, which the industry has determined to be most
critical for minimizing operating costs.
* Two-stage centrifugal compression-Two stages of
centrifugal compression enables more efﬁcient operation, at higher pressure ratios and especially in combination with an economizer.
* Economizer-Two compression stages also enables
the economizer cycle, where intermediate pressure gas
is injected into the second stage suction, also increasing
efﬁciency at the higher differential temperatures (pressure ratios)

IMAGE: DANFOSS

Coincident Industry Change

oil and its management.
The bet was that the market would value these beneﬁts enough to pay the premium that the combination
of technologies required. Historically, the HVAC market
in this capacity range had been signiﬁcantly driven by
product price, with little consideration for efﬁciency or
the other potential beneﬁts of alternatives; if it met the
code and/or customer requirements, then best price
won. This is in contrast to the larger capacity segments,
where customers were used to purchasing product
based on life-cycle cost, including the efﬁciency and
other beneﬁts in the long-term operating cost-driven
decision. The inventors of this technology were betting that there was an unserved 'latent" life-cycle cost
focused market in this mid-capacity HVAC segment.
They knew that the ﬁrst-cost focus was changing,
albeit slowly/regionally, based on a combination of
related regulatory and industry trend factors. The
regulatory trend factors included increasing efﬁciency
requirements along with the transition to non-ODP
refrigerants. The pace of these regulatory changes was
increasing, which along with rising energy costs and
environmental concerns drove more focus on the efﬁciency and long-term performance maintenance beneﬁts which this technology provides. They knew that the
https://www.ashrae.org
ASHRAE Journal - April 2020

Table of Contents for the Digital Edition of ASHRAE Journal - April 2020
