The rapid escalation of electricity prices has
created an opportunity to re-introduce gas-fired
air conditioning systems to the commercial building
market. In 1985 Gas Research Institute initiated a
program to develop an advanced gas engine-driven
water chiller. The packaged system has been
designed, fabricated and tested. A field experiment
unit has been operating since August, 1986, and
seven field test units have been operating since
April, 1987. The performance of the system has been
outstanding. The system should be an economically
attractive alternative to electrically-driven
chillers in most of the United States

Koplow, M. D.

Lindsay, B. B.

Texas A&M University

ALTERNATIVES TO ELECTRIC AIR CONDITIONING SYSTEMS 
BRUCE B. LINDSAY 
Pro jec t  Manager, Space Conditioning 
Gas Research I n s t i t u t e  
Chicago, I l l i n o i s  
ABSTRACT 
The rapid esca la t ion  of e l e c t r i c i t y  p r i c e s  has 
created an opportunity t o  re-introduce gas-fired 
a i r  conditioning systems t o  the  commercial bui lding 
market. In 1985 Gas Research I n s t i t u t e  i n i t i a t e d  a  
program t o  develop an advanced gas engine-driven 
water c h i l l e r .  The packaged system has been 
designed, fabr ica ted  and tes ted .  A f i e l d  experiment 
un i t  has  been operat ing s i n c e  August, 1986, and 
seven f i e l d  t e s t  u n i t s  have been operat ing s i n c e  
Apri l ,  1987. The performance of t h e  system has been 
outstanding. The system should be an economically 
a t t r a c t i v e  a l t e r n a t i v e  t o  e lec t r ica l ly -dr iven  
c h i l l e r s  i n  most of the United S t a t e s .  
INTRODUCTION 
Most l a rge  commercial bui ldings i n  the United 
S t a t e s  requ i re  a i r  conditioning (cooling) t o  provide 
a  comfortable environment f o r  tenants  and occupants. 
In addi t ion t o  t h e  loads imposed on bui ldings during 
the  summer, including s o l a r  gain and high ambient 
temperatures, t h e  a i r  condit ioning system must a l s o  
handle the  hea t  generated by l igh t ing ,  personnel,  
and o f f i c e  equipment. These i n t e r n a l  loads dominate 
i n  l a r g e  bui ldings,  e s p e c i a l l y  where there  a r e  l a r g e  
i n t e r n a l  zones r e l a t i v e  t o  exposed wal l  zones. 
The mechanical equipment t h a t  provides cool ing 
w i l l  vary s i g n i f i c a n t l y ,  depending on the  bui lding 
configurat ion,  owner/engineer preference, and l o c a l  
conditions. For the most p a r t ,  however, t h e  cooling 
system w i l l  u t i l i z e  an e l e c t r i c  motor-driven vapor 
compression device. E l e c t r i c  systems a r e  ubiqui tous,  
due t o  t h e i r  inherent  s impl ic i ty ,  r e l i a b i l i t y ,  
f l e x i b i l i t y ,  and e f f ic iency .  The a v a i l a b i l i t y  of 
low cos t  e l e c t r i c  power has equal ly supported the  
widespread acceptance of e l e c t r i c  a i r  conditioning. 
There a r e ,  of course, a l t e r n a t i v e  cool ing 
systems t h a t  u t i l i z e  o ther  energy sources, such a s  
n a t u r a l  gas o r  steam. In  t h e  e a r l y  days of a i r  
conditioning, these systems accounted f o r  near ly  
40X of the  i n s t a l l e d  capaci ty.  That share  has 
f a l l e n  t o  7% i n  t h e  Eightiee. The s t e a d i l y  
dec l in ing  c o s t  of e l e c t r i c i t y  and the  increase  i n  
cornpressor/motor performance was a  c r i t i c a l  f a c t o r  
i n  the reduction i n  a l t e r n a t i v e  cooling capaci ty.  
In  the l a s t  two decades, the  energy environment 
has undergone a  tremendous t r a n s i t i o n ,  espec ia l ly  
i n  the  e l e c t r i c  u t i l i t y  sec tor .  Pr io r  t o  1970, t h e  
e l e c t r i c  industry cons i s ten t ly  lowered i ts  cos t  t o  
generate e l e c t r i c i t y  with l a r g e  c e n t r a l  power p l a n t s  
and economies of s c a l e  production. Regulations 
influenced by Three Mile Is land and soaring i n t e r e s t  
r a t e e  have pushed the cost  of new generat ing 
capacity beyond t h e  range of many consumers. 
Certain u t i l i t i e s  have experienced " r a t e  shock". 
MICHAEL D. KOPLOW 
Director ,  Engine Technology 
TECOGEN Incorporated 
Waltham, Massachusetts 
40-90% increases  i n  e l e c t r i c i t y  p r i c e s ,  a s  new 
p l a n t s  a r e  brought on-line. Simultaneously, the 
n a t u r a l  gas indus t ry  has seen a  r e v e r s a l  i n  i ts 
pr ic ing ,  a s  increased competition with o i l  and 
"open access" have s t a b i l i z e d  the  market. The 
r e v e r s a l  i n  p r i c i n g  has created a  unique 
opportunity t o  market gas-f i red cool ing systems. 
Figure 1 i l l u s t r a t e s  these  t rends.  
GAS COOLING SYSTEMS 
Gas-fueled a i r  condit ioning systems have been 
synonymous with absorpt ion c h i l l e r s .  C a r r i e r ,  York, 
Trane, and Arkla Serve1 manufactured a  l i n e  of u n i t s  
i n  the e a r l y  S i x t i e s  based upon a  s ing le -e f fec t  
cycle ,  which achieved a  c o e f f i c i e n t  of performance 
(COP) of 0.70. These packages, with the  exception 
of York, a r e  s t i l l  ava i lab le .  The Japanese have 
developed d i r e c t - f i r e d  double-effect absorpt ion 
c h i l l e r s  tha t  a r e  40% more e f f i c i e n t  than t h e  
s ing le -e f fec t  predecessors (COP of 0.92-1.0). 
Hitachi ,  Yazaki, and Sanyo a r e  cur ren t ly  marketing 
products i n  t h e  United S t a t e s .  Absorption c h i l l e r s  
a r e  pene t ra t ing  c e r t a i n  regions of t h e  United 
S t a t e s ,  and they have been increas ing ly  employed 
with cogeneration systems, which have l a r g e  amounts 
of waste heat  t o  d r i v e  t h e  c h i l l e r .  Unfortunately, 
t h e  l a r g e  heat  t r a n s f e r  sur face  required f o r  the  
absorption process imposes a  high f i r s t  cos t  
penal ty and many engineers  a r e  h e s i t a n t  t o  i n s t a l l  
these  packages. 
Absorption c h i l l e r s  a r e  not t h e  only 1. 
gas-fueled cooling systems. Engine-driven 
compression cool ing packages and desiccant  
dehumidification systems a r e  now a v a i l a b l e  f o r  
commercial bui ldings.  Engine-driven c h i l l e r s  
compete d i r e c t l y  with e l e c t r i c  a i r  condit ioning 
systems and w i l l  be discussed f u r t h e r .  
GAS ENGINE-DRIVEN COOLING 
The concept of an engine-driven c h i l l e r  is 
very fundamental. The e l e c t r i c  motor: which d r i v e s  
t h e  r e f r i g e r a n t  compressor, is replaced with an 
engine. (Each prime mover has  a  s h a f t  t h a t  r o t a t e s  
and t ransmits  power.) Gas engine-driven c h i l l e r s  
can c a p i t a l i z e  on t h e  advances i n  compressor 
technology t h a t  have made e l e c t r i c  a i r  condit ioning 
so  a t t r a c t i v e .  The r e l a t i v e  p r i c e s  of n a t u r a l  gas 
and e l e c t r i c i t y  w i l l  determine the  bes t  choice. An 
e l e c t r i c  c h i l l e r  may have a  COP of 5.5. The gas 
engine c h i l l e r ,  because i t s  engine is approximately 
30% (HHV) e f f i c i e n t ,  w i l l  have a  COP of 1.6-1.7. 
I f  t h e  e l e c t r i c / g a s  p r i c e  r a t i o  i s  g r e a t e r  than 
3.33, t h e  gas c h i l l e r  w i l l  c o s t  l e e s  t o  operate .  
This  simple s u b s t i t u t i o n  is  much more complex 
i n  r e a l i t y .  
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1. The compressor choices are limited to an 
open drive, which has mechanical seals 
that are subject to wear. 
2. The compressor is typically designed to 
operate with electric motors at 1800 rpm 
or 3600 rpm. The gaa engine may have to 
be coupled with a gearbox to increase 
shaft speed. 
3. Gas engines are typically larger than 
electric motors and subject to vibration 
and torque fluctuations. 
4. Oil and spark plug changes, timing 
adjustments, valve wear, and coolant 
replacement add considerable cost to the 
chiller's operation. 
Despite these obstacles, the engine chiller 
possesses certain attributes that makes it very 
attractive: 
1. The engine can vary its speed and load, 
which permits the chiller to modulate 
very effectively. The part load 
performance of the gas engine chiller is 
superior, relative to electric systems. 
2. The engine can operate above rated capacity 
for short periods, reducing the total 
capacity required for an installation. 
3. Waste heat from the engine can be recovered 
for domestic water heating, process 
applications, and additional cooling 
capacity, if integrated with absorption 
or desiccant equipment. 
TECOCHILL CH-150 
In 1985 the Gas Research Institute initiated a 
program to develop a nominal 150 ton gas-fueled 
engine-driven water chiller for commercial buildings. 
The packaged system has been designed, fabricated, 
and operated satisfactorily in the laboratory and 
in a 450-bed hospital. Figure 2 illustrates the 
original prototype design that was experimentally 
installed at Elliot Hospital in Manchester. 
New Hampshire, to evaluate actual system operations 
and installation procedures. The chiller system. 
including the absorption package, exhibited an 
average COP approaching 2.0. The preliminary 
results of the field experiment were integrated into 
a new design that radically simplified the package . 
and improved its performance. 
The engine chiller has produced 150 tons of 
cooling at a COP of 1.4 at ARI full load conditions. 
The heat from the engine may be recovered to drive 
an optional absorption chiller package, providing 
an additional 35 tons of cooling and increasing 
the system COP to 1.75. The system is comprised of 
a 454 cubic inch G.M. engine, modified for 
stationary duty, a Howden twin screw compressor, 
and advanced microprocessor controls. The engine 
chiller, by capitalizing on available vapor 
compression equipment and low cost automotive 
engines, can meet a highly competitive cost goal of 
less than $400/ton. The engine's ability to vary 
speed greatly improves the performance of the 
compressor at part load. The engine chiller has an 
ARI Integrated Part Load Value (IPLV) of 1.7. 
Figure 3 exhibits the part load curve for the 
engine chiller. Further, the engine can be operated 
above design speeds (up to 3600 rpm) for short 
periods to provide additional peaking capacity. 
The engine chiller incorporates an advanced 
microprocessor-based controller that monitors 
compressor and engine functions. The system 
permits the engine to start and "warm up" prior to 
loading the compreseor. The controller can be 
connected by modem to remote sites for monitoring 
and operation. This feature and the internal 
diagnostics capability reduce nuisance outages and 
can significantly reduce maintenance costs. In 
addition, the low cost engine can be replaced. 
rather than repaired, further reducing down tire. 
The new design, shown in Figure 4, waa tested 
in a seven unit field test during the summer of 
1987. The prototype chillers were installed in a 
variety of comercial buildings, including hotels, 
office buildings, apartment buildings, and 
manufacturing facilities. The units have 
demonstrated a fleet availability of 96% with over 
9,200 hours of operation. The average COP ranged 
from 1.09 to 1.86. depending upon the load profile 
and outdoor temperatures. Minor design prob1en.s 
were identified and the packages were modified. 
The microprocessor-based controller permitted 
remote monitoring and operation as well as serving 
as the data acquisition system during the field 
test. Site owners have reported a high degree of 
satisfaction. 
Bleyle of America, located in Shenandoah. 
Georgia, is one of the field test sites. The 
manufacturing firm produces fine women's apparel. 
The engine chiller replaced an external chilled 
water supply that had experienced poor availability, 
forcing Bleyle to utilize electric rooftop cooling 
systems. The high latent loads from the steam 
presses and personnel were easily met by the engine 
chiller while avoiding nearly 110 kW of electric 
demand. 
PROSPECTS FOR GAS COOLING 
Market assessments and economic analyses have 
demonstrated that a huge potential for gas-fueled 
engine-driven cooling systems exists, especially 
in regions of the U.S. that have high electric 
demand charges. Demand charges can constitute 
approximately half the operating cost for an 
electric chiller. Figure 5 illustrates the 
difference in operating costs for an electric and 
gas 150 ton chiller in the Chicago area based on 
current rates. Figure 6 exhibits the cities 
within the United States with attractive econm.ics. 
The cities are plotted by the electric demand and 
energy charges of the city's major utility. The 
diagonal line represents a three year payback for 
the incremental investment above an electric 
centrifugal chiller. All cities above the line 
have shorter paybacks. Several gas utilities offer 
rebates of $100-$280/ton to commercial customers 
that install gas cooling systems, further reducing 
the first cost premium. 
Although the engine chiller will be competitive 
(on life cycle costs) with electric chillers in the 
new construction market, the real opportunity for 
penetration is in the replacement market. 
Commercial building developers are particularly 
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Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 1988
s e n s i t i v e  t o  f i r s t  c o s t s ,  almost t o  t h e  exclusion 
of other  considerat ions.  Owners, on t h e  o ther  hand, 
a r e  more w i l l i n g  t o  consider the  long-term operat ing 
costs .  I f  the  owner has two or more e l e c t r i c  
c h i l l e r s ,  which is  t y p i c a l  of many i n s t a l l a t i o n s ,  
he can replace one e l e c t r i c  c h i l l e r  with the  gas 
c h i l l e r  and operate  t h e  u n i t s  i n  t h e  most 
advantageous s t ra tegy .  The superior  part-load 
performance of t h e  engine c h i l l e r ,  coupled with i ts  
minimal e l e c t r i c  requirements, makes it an i d e a l  
peaking un i t .  In regions with high energy c o s t s ,  
i t  may be b e n e f i c i a l  t o  base load the  gas c h i l l e r  
and peak with t h e  e l e c t r i c  c h i l l e r .  
Gas-fueled cooling systems can provide 
s i g n i f i c a n t  benef i t s  t o  e l e c t r i c  u t i l i t i e s  and 
ratepayers. Connnercial cooling may account f o r  up 
t o  40% of a u t i l i t y ' s  peak demand. A s  capaci ty 
margins a r e  consumed, gas cooling may a c t u a l l y  
reduce peak e l e c t r i c  demand growth f o r  u t i l i t i e s  
and defe r  investment i n  new generating capaci ty.  
SPECIAL APPLICATIONS 
Humidity is a prominent concern i n  commercial 
bui ldings espec ia l ly  i n  c r i t i c a l  environments, 
such a s  hosp i ta l s  o r  computer cen te rs .  In 
conventional e l e c t r i c  a i r  conditioning systems, the  
customary approach t o  reducing humidity l e v e l s  
u t i l i z e s  low temperature water t o  supercool t h e  
incoming a i r  stream. Water moisture condenses out  
a t  t h e  lower dewpoint, reducing humidity, but the 
a i r  stream must be reheated t o  temper t h e  a i r .  
This approach is very expensive, i n  t h a t  the  
compressor requ i res  g r e a t e r  energy t o  produce t h e  
lower temperature water and energy is required f o r  
the terminal reheat .  The engine c h i l l e r  has the  
a b i l i t y  t o  produce low temperature c h i l l e d  water,  
plus  the  benef i t  of hot water recovery, which can 
be applied t o  dehumidification processes. 
The recovered hot water from t h e  engine c h i l l e r  
c a l  a l s o  be used t o  regenerate  a desiccant  mate r ia l .  
Desiccants adsorb moisture from t h e  conditioned a i r  
stream, reducing humidity l e v e l s .  The "wet" 
desiccant  is cycled out of t h e  a i r  stream, heated, 
and exposed t o  a purge a i r  stream t o  remove t h e  
moisture. The d r i e r  a i r  e l imina tes  the  need f o r  low 
evaporator temperatures, allowing the  compressor 
t o  operate more e f f i c i e n t l y ,  providing only s e n s i b l e  
cooling. The synergy of the  desiccant /engine 
c h i l l e r  system has g r e a t  p o t e n t i a l  t o  maintain 
higher comfort l e v e l s  a t  equal  o r  lower c o s t s  
r e l a t i v e  t o  conventional e l e c t r i c  systems. 
FUTURE PRODUCTS 
The development program has been expanded t o  
a range of gas engine-driven cooling systems from 
15-ton d i r e c t  expansion rooftop packages t o  500-ton 
l iqu id  c h i l l e r s .  Addit ional ly,  an in tegra ted  
engine c h i l l e r / d e s i c c a n t  dehumidification system 
and an engine c h i l l e r l i c e  s to rage  system a r e  being 
developed, which should grea t ly  improve occupant 
comfort while reducing energy cos t s .  
Gas engine-driven rooftop packages a r e  under 
development by TECOGEN Inc. ,  and American Gas 
Association Laboratories. TECOGEN is  i n t e g r a t i n g  
a 3.0 l i t e r  General Motors engine with a Car r ie r  
compressor and a i r  handling package. AGA Labs is  
i n t e g r a t i n g  a Hercules engine with a Thermo King 
compressor. The package c a p a c i t i e s  a r e  25 and 15 
tons respec t ive ly .  The concept is i l l u s t r a t e d  i n  
Figure 6.  
TECOGEN has fabr ica ted  a 500-ton l i q u i d  
c h i l l e r  based on a dua l  c e n t r i f u g a l  compressor 
c h i l l e r  package from Car r ie r .  Each 250-ton 
compressor w i l l  be dr iven by a 454 cubic inch 
General Motors engine. A COP of 1.8 is targeted 
and t h e  f i r s t  c o s t  premium should be very low. 
The engines can vary speed from 2200 rpm t o  
3000 rpm and t h e  engine-compressors can be operated 
ind iv idua l ly  t o  provide extremely a t t r a c t i v e  p a r t  
load operation. The 500-ton c h i l l e r  is shown i n  
Figure 8 .  
The 150-ton engine-driven c h i l l e r  package 
w i l l  be commercially a v a i l a b l e  i n  1988. Forty 
u n i t s  have been ordered f o r  1988 de l ivery  by a 
consortium of gas u t i l i t i e s .  The 500-ton package 
and engine-driven u n i t a r y  packages should be 
a v a i l a b l e  i n  1990. 
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Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 1988
Figure 1 .  E l e c t r i c  and Natural Gas Pric ing 
5051 52535455565758596061 62636465666768687071727374757677787B808182838485 
GAS + ELECTRIC 0 PDJGAS A PDJ ELEC 
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Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 1988
Figure 2. Engine-Driven Chiller with Absorption 
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Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 1988
Figure 3. Part Load Performance (COP) 
Electric vs. Gas Engine 
System COP 
10 20 30 40 5 0  6 0  70 80 90 100 
Part Load(%) 
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Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 1988
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Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 1988
Figure 5 .  Typical  Operating Costs  
E l e c t r i c  v s .  Gas Engine 
S - Dollan 
Malnlmance 
0 Aux. Energy 
Aux.  erna and 
Compressor Gas 
Compressor Energy 
Compressor Demand 
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Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 1988
Figure 6. Sensitivity to First Cost 
Electric Energy Cost (*/kwh) 
3 - 
2 - 
1 - 
0 2 4 6 8 10 12 14 16 18 20  22 24 
Demand Charge (S/kw) 
Summer, 1985 Rater, Large Commercial Bulldlngr. No Taxea or Surcharge@ Included 
Ratchet Charge# Applicable 
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Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 1988
Figure 7 .  Engine-Driven Rooftop HGAC Package 
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Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 1988
F i p r e  6 .  500 Ton Engine-Driven Chi . l l e r  
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Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 1988


English

Alternatives to Electric Air Conditioning Systems

Texas A&amp;M Repository

ALTERNATIVES TO ELECTRIC AIR CONDITIONING SYSTEMS BRUCE B. LINDSAY Pro jec t  Manager, Space Conditioning Gas Research I n s t i t u t e  Chicago, I l l i n o i s  ABSTRACT The rapid esca la t ion  of e l e c t r i c i t y  p r i c e s  has created an opportunity t o  re-introduce gas-fired a i r  conditioning systems t o  the  commercial bui lding market. In 1985 Gas Research I n s t i t u t e  i n i t i a t e d  a  program t o  develop an advanced gas engine-driven water c h i l l e r .  The packaged system has been designed, fabr ica ted  and tes ted .  A f i e l d  experiment un i t  has  been operat ing s i n c e  August, 1986, and seven f i e l d  t e s t  u n i t s  have been operat ing s i n c e  Apri l ,  1987. The performance of t h e  system has been outstanding. The system should be an economically a t t r a c t i v e  a l t e r n a t i v e  t o  e lec t r ica l ly -dr iven  c h i l l e r s  i n  most of the United S t a t e s .  INTRODUCTION Most l a rge  commercial bui ldings i n  the United S t a t e s  requ i re  a i r  conditioning (cooling) t o  provide a  comfortable environment f o r  tenants  and occupants. In addi t ion t o  t h e  loads imposed on bui ldings during the  summer, including s o l a r  gain and high ambient temperatures, t h e  a i r  condit ioning system must a l s o  handle the  hea t  generated by l igh t ing ,  personnel,  and o f f i c e  equipment. These i n t e r n a l  loads dominate i n  l a r g e  bui ldings,  e s p e c i a l l y  where there  a r e  l a r g e  i n t e r n a l  zones r e l a t i v e  t o  exposed wal l  zones. The mechanical equipment t h a t  provides cool ing w i l l  vary s i g n i f i c a n t l y ,  depending on the  bui lding configurat ion,  owner/engineer preference, and l o c a l  conditions. For the most p a r t ,  however, t h e  cooling system w i l l  u t i l i z e  an e l e c t r i c  motor-driven vapor compression device. E l e c t r i c  systems a r e  ubiqui tous,  due t o  t h e i r  inherent  s impl ic i ty ,  r e l i a b i l i t y ,  f l e x i b i l i t y ,  and e f f ic iency .  The a v a i l a b i l i t y  of low cos t  e l e c t r i c  power has equal ly supported the  widespread acceptance of e l e c t r i c  a i r  conditioning. There a r e ,  of course, a l t e r n a t i v e  cool ing systems t h a t  u t i l i z e  o ther  energy sources, such a s  n a t u r a l  gas o r  steam. In  t h e  e a r l y  days of a i r  conditioning, these systems accounted f o r  near ly  40X of the  i n s t a l l e d  capaci ty.  That share  has f a l l e n  t o  7% i n  t h e  Eightiee. The s t e a d i l y  dec l in ing  c o s t  of e l e c t r i c i t y  and the  increase  i n  cornpressor/motor performance was a  c r i t i c a l  f a c t o r  i n  the reduction i n  a l t e r n a t i v e  cooling capaci ty.  In  the l a s t  two decades, the  energy environment has undergone a  tremendous t r a n s i t i o n ,  espec ia l ly  i n  the  e l e c t r i c  u t i l i t y  sec tor .  Pr io r  t o  1970, t h e  e l e c t r i c  industry cons i s ten t ly  lowered i ts  cos t  t o  generate e l e c t r i c i t y  with l a r g e  c e n t r a l  power p l a n t s  and economies of s c a l e  production. Regulations influenced by Three Mile Is land and soaring i n t e r e s t  r a t e e  have pushed the cost  of new generat ing capacity beyond t h e  range of many consumers. Certain u t i l i t i e s  have experienced " r a t e  shock". MICHAEL D. KOPLOW Director ,  Engine Technology TECOGEN Incorporated Waltham, Massachusetts 40-90% increases  i n  e l e c t r i c i t y  p r i c e s ,  a s  new p l a n t s  a r e  brought on-line. Simultaneously, the n a t u r a l  gas indus t ry  has seen a  r e v e r s a l  i n  i ts pr ic ing ,  a s  increased competition with o i l  and "open access" have s t a b i l i z e d  the  market. The r e v e r s a l  i n  p r i c i n g  has created a  unique opportunity t o  market gas-f i red cool ing systems. Figure 1 i l l u s t r a t e s  these  t rends.  GAS COOLING SYSTEMS Gas-fueled a i r  condit ioning systems have been synonymous with absorpt ion c h i l l e r s .  C a r r i e r ,  York, Trane, and Arkla Serve1 manufactured a  l i n e  of u n i t s  i n  the e a r l y  S i x t i e s  based upon a  s ing le -e f fec t  cycle ,  which achieved a  c o e f f i c i e n t  of performance (COP) of 0.70. These packages, with the  exception of York, a r e  s t i l l  ava i lab le .  The Japanese have developed d i r e c t - f i r e d  double-effect absorpt ion c h i l l e r s  tha t  a r e  40% more e f f i c i e n t  than t h e  s ing le -e f fec t  predecessors (COP of 0.92-1.0). Hitachi ,  Yazaki, and Sanyo a r e  cur ren t ly  marketing products i n  t h e  United S t a t e s .  Absorption c h i l l e r s  a r e  pene t ra t ing  c e r t a i n  regions of t h e  United S t a t e s ,  and they have been increas ing ly  employed with cogeneration systems, which have l a r g e  amounts of waste heat  t o  d r i v e  t h e  c h i l l e r .  Unfortunately, t h e  l a r g e  heat  t r a n s f e r  sur face  required f o r  the  absorption process imposes a  high f i r s t  cos t  penal ty and many engineers  a r e  h e s i t a n t  t o  i n s t a l l  these  packages. Absorption c h i l l e r s  a r e  not t h e  only 1. gas-fueled cooling systems. Engine-driven compression cool ing packages and desiccant  dehumidification systems a r e  now a v a i l a b l e  f o r  commercial bui ldings.  Engine-driven c h i l l e r s  compete d i r e c t l y  with e l e c t r i c  a i r  condit ioning systems and w i l l  be discussed f u r t h e r .  GAS ENGINE-DRIVEN COOLING The concept of an engine-driven c h i l l e r  is very fundamental. The e l e c t r i c  motor: which d r i v e s  t h e  r e f r i g e r a n t  compressor, is replaced with an engine. (Each prime mover has  a  s h a f t  t h a t  r o t a t e s  and t ransmits  power.) Gas engine-driven c h i l l e r s  can c a p i t a l i z e  on t h e  advances i n  compressor technology t h a t  have made e l e c t r i c  a i r  condit ioning so  a t t r a c t i v e .  The r e l a t i v e  p r i c e s  of n a t u r a l  gas and e l e c t r i c i t y  w i l l  determine the  bes t  choice. An e l e c t r i c  c h i l l e r  may have a  COP of 5.5. The gas engine c h i l l e r ,  because i t s  engine is approximately 30% (HHV) e f f i c i e n t ,  w i l l  have a  COP of 1.6-1.7. I f  t h e  e l e c t r i c / g a s  p r i c e  r a t i o  i s  g r e a t e r  than 3.33, t h e  gas c h i l l e r  w i l l  c o s t  l e e s  t o  operate .  This  simple s u b s t i t u t i o n  is  much more complex i n  r e a l i t y .  ESL-HH-88-09-23Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 19881. The compressor choices are limited to an open drive, which has mechanical seals that are subject to wear. 2. The compressor is typically designed to operate with electric motors at 1800 rpm or 3600 rpm. The gaa engine may have to be coupled with a gearbox to increase shaft speed. 3. Gas engines are typically larger than electric motors and subject to vibration and torque fluctuations. 4. Oil and spark plug changes, timing adjustments, valve wear, and coolant replacement add considerable cost to the chiller's operation. Despite these obstacles, the engine chiller possesses certain attributes that makes it very attractive: 1. The engine can vary its speed and load, which permits the chiller to modulate very effectively. The part load performance of the gas engine chiller is superior, relative to electric systems. 2. The engine can operate above rated capacity for short periods, reducing the total capacity required for an installation. 3. Waste heat from the engine can be recovered for domestic water heating, process applications, and additional cooling capacity, if integrated with absorption or desiccant equipment. TECOCHILL CH-150 In 1985 the Gas Research Institute initiated a program to develop a nominal 150 ton gas-fueled engine-driven water chiller for commercial buildings. The packaged system has been designed, fabricated, and operated satisfactorily in the laboratory and in a 450-bed hospital. Figure 2 illustrates the original prototype design that was experimentally installed at Elliot Hospital in Manchester. New Hampshire, to evaluate actual system operations and installation procedures. The chiller system. including the absorption package, exhibited an average COP approaching 2.0. The preliminary results of the field experiment were integrated into a new design that radically simplified the package . and improved its performance. The engine chiller has produced 150 tons of cooling at a COP of 1.4 at ARI full load conditions. The heat from the engine may be recovered to drive an optional absorption chiller package, providing an additional 35 tons of cooling and increasing the system COP to 1.75. The system is comprised of a 454 cubic inch G.M. engine, modified for stationary duty, a Howden twin screw compressor, and advanced microprocessor controls. The engine chiller, by capitalizing on available vapor compression equipment and low cost automotive engines, can meet a highly competitive cost goal of less than $400/ton. The engine's ability to vary speed greatly improves the performance of the compressor at part load. The engine chiller has an ARI Integrated Part Load Value (IPLV) of 1.7. Figure 3 exhibits the part load curve for the engine chiller. Further, the engine can be operated above design speeds (up to 3600 rpm) for short periods to provide additional peaking capacity. The engine chiller incorporates an advanced microprocessor-based controller that monitors compressor and engine functions. The system permits the engine to start and "warm up" prior to loading the compreseor. The controller can be connected by modem to remote sites for monitoring and operation. This feature and the internal diagnostics capability reduce nuisance outages and can significantly reduce maintenance costs. In addition, the low cost engine can be replaced. rather than repaired, further reducing down tire. The new design, shown in Figure 4, waa tested in a seven unit field test during the summer of 1987. The prototype chillers were installed in a variety of comercial buildings, including hotels, office buildings, apartment buildings, and manufacturing facilities. The units have demonstrated a fleet availability of 96% with over 9,200 hours of operation. The average COP ranged from 1.09 to 1.86. depending upon the load profile and outdoor temperatures. Minor design prob1en.s were identified and the packages were modified. The microprocessor-based controller permitted remote monitoring and operation as well as serving as the data acquisition system during the field test. Site owners have reported a high degree of satisfaction. Bleyle of America, located in Shenandoah. Georgia, is one of the field test sites. The manufacturing firm produces fine women's apparel. The engine chiller replaced an external chilled water supply that had experienced poor availability, forcing Bleyle to utilize electric rooftop cooling systems. The high latent loads from the steam presses and personnel were easily met by the engine chiller while avoiding nearly 110 kW of electric demand. PROSPECTS FOR GAS COOLING Market assessments and economic analyses have demonstrated that a huge potential for gas-fueled engine-driven cooling systems exists, especially in regions of the U.S. that have high electric demand charges. Demand charges can constitute approximately half the operating cost for an electric chiller. Figure 5 illustrates the difference in operating costs for an electric and gas 150 ton chiller in the Chicago area based on current rates. Figure 6 exhibits the cities within the United States with attractive econm.ics. The cities are plotted by the electric demand and energy charges of the city's major utility. The diagonal line represents a three year payback for the incremental investment above an electric centrifugal chiller. All cities above the line have shorter paybacks. Several gas utilities offer rebates of $100-$280/ton to commercial customers that install gas cooling systems, further reducing the first cost premium. Although the engine chiller will be competitive (on life cycle costs) with electric chillers in the new construction market, the real opportunity for penetration is in the replacement market. Commercial building developers are particularly ESL-HH-88-09-23Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 1988s e n s i t i v e  t o  f i r s t  c o s t s ,  almost t o  t h e  exclusion of other  considerat ions.  Owners, on t h e  o ther  hand, a r e  more w i l l i n g  t o  consider the  long-term operat ing costs .  I f  the  owner has two or more e l e c t r i c  c h i l l e r s ,  which is  t y p i c a l  of many i n s t a l l a t i o n s ,  he can replace one e l e c t r i c  c h i l l e r  with the  gas c h i l l e r  and operate  t h e  u n i t s  i n  t h e  most advantageous s t ra tegy .  The superior  part-load performance of t h e  engine c h i l l e r ,  coupled with i ts  minimal e l e c t r i c  requirements, makes it an i d e a l  peaking un i t .  In regions with high energy c o s t s ,  i t  may be b e n e f i c i a l  t o  base load the  gas c h i l l e r  and peak with t h e  e l e c t r i c  c h i l l e r .  Gas-fueled cooling systems can provide s i g n i f i c a n t  benef i t s  t o  e l e c t r i c  u t i l i t i e s  and ratepayers. Connnercial cooling may account f o r  up t o  40% of a u t i l i t y ' s  peak demand. A s  capaci ty margins a r e  consumed, gas cooling may a c t u a l l y  reduce peak e l e c t r i c  demand growth f o r  u t i l i t i e s  and defe r  investment i n  new generating capaci ty.  SPECIAL APPLICATIONS Humidity is a prominent concern i n  commercial bui ldings espec ia l ly  i n  c r i t i c a l  environments, such a s  hosp i ta l s  o r  computer cen te rs .  In conventional e l e c t r i c  a i r  conditioning systems, the  customary approach t o  reducing humidity l e v e l s  u t i l i z e s  low temperature water t o  supercool t h e  incoming a i r  stream. Water moisture condenses out  a t  t h e  lower dewpoint, reducing humidity, but the a i r  stream must be reheated t o  temper t h e  a i r .  This approach is very expensive, i n  t h a t  the  compressor requ i res  g r e a t e r  energy t o  produce t h e  lower temperature water and energy is required f o r  the terminal reheat .  The engine c h i l l e r  has the  a b i l i t y  t o  produce low temperature c h i l l e d  water,  plus  the  benef i t  of hot water recovery, which can be applied t o  dehumidification processes. The recovered hot water from t h e  engine c h i l l e r  c a l  a l s o  be used t o  regenerate  a desiccant  mate r ia l .  Desiccants adsorb moisture from t h e  conditioned a i r  stream, reducing humidity l e v e l s .  The "wet" desiccant  is cycled out of t h e  a i r  stream, heated, and exposed t o  a purge a i r  stream t o  remove t h e  moisture. The d r i e r  a i r  e l imina tes  the  need f o r  low evaporator temperatures, allowing the  compressor t o  operate more e f f i c i e n t l y ,  providing only s e n s i b l e  cooling. The synergy of the  desiccant /engine c h i l l e r  system has g r e a t  p o t e n t i a l  t o  maintain higher comfort l e v e l s  a t  equal  o r  lower c o s t s  r e l a t i v e  t o  conventional e l e c t r i c  systems. FUTURE PRODUCTS The development program has been expanded t o  a range of gas engine-driven cooling systems from 15-ton d i r e c t  expansion rooftop packages t o  500-ton l iqu id  c h i l l e r s .  Addit ional ly,  an in tegra ted  engine c h i l l e r / d e s i c c a n t  dehumidification system and an engine c h i l l e r l i c e  s to rage  system a r e  being developed, which should grea t ly  improve occupant comfort while reducing energy cos t s .  Gas engine-driven rooftop packages a r e  under development by TECOGEN Inc. ,  and American Gas Association Laboratories. TECOGEN is  i n t e g r a t i n g  a 3.0 l i t e r  General Motors engine with a Car r ie r  compressor and a i r  handling package. AGA Labs is  i n t e g r a t i n g  a Hercules engine with a Thermo King compressor. The package c a p a c i t i e s  a r e  25 and 15 tons respec t ive ly .  The concept is i l l u s t r a t e d  i n  Figure 6.  TECOGEN has fabr ica ted  a 500-ton l i q u i d  c h i l l e r  based on a dua l  c e n t r i f u g a l  compressor c h i l l e r  package from Car r ie r .  Each 250-ton compressor w i l l  be dr iven by a 454 cubic inch General Motors engine. A COP of 1.8 is targeted and t h e  f i r s t  c o s t  premium should be very low. The engines can vary speed from 2200 rpm t o  3000 rpm and t h e  engine-compressors can be operated ind iv idua l ly  t o  provide extremely a t t r a c t i v e  p a r t  load operation. The 500-ton c h i l l e r  is shown i n  Figure 8 .  The 150-ton engine-driven c h i l l e r  package w i l l  be commercially a v a i l a b l e  i n  1988. Forty u n i t s  have been ordered f o r  1988 de l ivery  by a consortium of gas u t i l i t i e s .  The 500-ton package and engine-driven u n i t a r y  packages should be a v a i l a b l e  i n  1990. ESL-HH-88-09-23Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 1988Figure 1 .  E l e c t r i c  and Natural Gas Pric ing 5051 52535455565758596061 62636465666768687071727374757677787B808182838485 GAS + ELECTRIC 0 PDJGAS A PDJ ELEC ESL-HH-88-09-23Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 1988Figure 2. Engine-Driven Chiller with Absorption ESL-HH-88-09-23Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 1988Figure 3. Part Load Performance (COP) Electric vs. Gas Engine System COP 10 20 30 40 5 0  6 0  70 80 90 100 Part Load(%) ESL-HH-88-09-23Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 1988ESL-HH-88-09-23Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 1988Figure 5 .  Typical  Operating Costs  E l e c t r i c  v s .  Gas Engine S - Dollan Malnlmance 0 Aux. Energy Aux.  erna and Compressor Gas Compressor Energy Compressor Demand ESL-HH-88-09-23Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 1988Figure 6. Sensitivity to First Cost Electric Energy Cost (*/kwh) 3 - 2 - 1 - 0 2 4 6 8 10 12 14 16 18 20  22 24 Demand Charge (S/kw) Summer, 1985 Rater, Large Commercial Bulldlngr. No Taxea or Surcharge@ Included Ratchet Charge# Applicable ESL-HH-88-09-23Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 1988Figure 7 .  Engine-Driven Rooftop HGAC Package ESL-HH-88-09-23Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 1988F i p r e  6 .  500 Ton Engine-Driven Chi . l l e r  ESL-HH-88-09-23Proceedings of the Fifth Symposium on Improving Building Systems in Hot and Humid Climates, Houston, TX, September 12-14, 1988

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Alternatives to Electric Air Conditioning Systems

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Texas A&M University

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Alternatives to Electric Air Conditioning Systems

Abstract

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Texas A&M University

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