Also highly recommended in our analysis
was enthalpy wheel energy recovery with
a heat-recovery chiller for pre-cooling
and reheat (Figure 4). In Singapore, this
configuration saved nearly 130,000 k Wh/
yr compared with the base case, though it
did also have the highest first-cost ranking.
In Houston, annual k Wh savings were
modeled at 83,982. The design delivered
slightly better energy savings in Singapore
and Chicago than in Atlanta and Houston,
but still outpaced all the remaining options
for the four zones studied, delivering energy
savings of more than 50% versus base case.
Recommended options were an enthalpy
wheel energy-recovery system with electric
reheat (100% exhaust through the wheel)
and a wrap-around heat pipe system with no
reheat. Both designs resulted in annual savings
of more than 72,000 k Wh in Singapore versus
the base case, and yielded an energy reduction
of about 35% a year for that location with
fairly low first costs. Of these two recommend-
ed options, the wheel with electric reheat
(Figure 5) was superior to the wrap-around
heat pipe (Figure 6) in Chicago and Atlanta,
Maintenance is required, but the incoming
and outgoing airflow need not be adjacent.
Thus, these systems can be particularly useful
for retrofits.
Given these choices, what energy-recovery
option makes the most sense for your lab?
Our firm recently analyzed eight options for
lab HVAC systems in Singapore, Houston,
The energy-recovery options we studied
• Enthalpy wheel with electric reheat
(100% exhaust through wheel).
• Heat pipe with electric reheat.
• Heat pipe with evaporative pre-cool
and electric reheat.
• Wrap-around heat pipe (no reheat).
• Enthalpy wheel with passive desiccant wheel and no reheat (100% exhaust
through wheel).
• Enthalpy wheel with passive desiccant
wheel and no reheat (70% exhaust through
wheel).
• Enthalpy wheel with passive desiccant
wheel and no reheat (45% exhaust through
wheel).
• Enthalpy wheel with heat recovery
chiller for pre-cool and reheat.
Interestingly, though the locations we analyzed were diverse in terms of climate, the options we identified as “highly recommended,”
based on energy-reduction potential, were the
same for all four areas we studied (Figure 2).
Schematics for the four best-rated options are
shown in Figures 3 through 6.
The enthalpy wheel energy recovery with
a passive desiccant wheel and no reheat
(100% exhaust through the wheel, shown in
Figure 3) was rated as highly recommended
for all four climates. For the hot and humid
weather of Singapore, this choice yielded
more than 144,000 k Wh/yr in electric energy savings versus the base case. For Houston, annual modeled savings were 91,254
k Wh/yr. The dual-wheel system actually
offered energy savings of around 60% per
70% in Chicago, making it the top choice
across the board.
where the cooling season is shorter and less
severe. Performance of the heat pipe was fairly
similar to the wheel-plus-reheat configuration
in both Singapore and Houston. For instance,
in Houston, the wheel-plus-reheat combination yielded annual electric energy savings of
44,759 k Wh, compared with 43,254 k Wh for
the wrap-around heat pipe system.
In conclusion, it’s generally best to explore
all lower levels of the pyramid before reaching
for higher levels. The top level, renewable
energy, isn’t discussed in this article, but may
be an option for some labs. In particular, solar
power is growing in feasibility as photovoltaic technology continues to improve and
costs continue to drop. Energy recovery is
now code-mandated in many instances, and
the best solutions in this category will vary.
Climate remains an important factor affecting
HVAC design decisions for lab facilities.
Careful research and analysis will pay off in
long-term energy and cost savings.
Daniel L. Doyle, PE, is chairman of Grumman/Butkus Associates, a firm of energy-ef-ficiency consultants and sustainability design
engineers based in Evanston, Ill.
Energy-efficient HVAC for
labs in hot, humid climates
continued from page 14
Figure 5: An enthalpy wheel with electric reheat delivered very good results in Chicago, and acceptable
results in warmer, wetter climates, though not as good as some other choices.
Figure 6: A wrap-around heat pipe system with no reheat performed fairly well in Singapore, and delivered
some savings in Atlanta and Houston, but was relatively unimpressive when modeled for Chicago.
