Energy Efficiency and Energy
Recovery
Fresh air is essential to healthy people –
and healthy buildings. That’s why commercial
buildings are required to bring in fresh air –
typically 15-20 cubic feet per minute (cfm) for every
occupant. This unconditioned air greatly increases
your building’s air-conditioning load –
and since an equal amount of air must be vented outdoors,
you’re basically “throwing away”
air you’ve paid to cool.
Energy recovery ventilation systems – or “ERVs”
– help reduce this waste and lower your energy
costs. What’s more, an FPL incentive program
now helps businesses pay for this technology –
so you can save even more when you install a qualifying
ERV unit on a new or existing HVAC system.
Energy recovery systems typically incorporate heat
exchange equipment to reduce energy costs by extracting
heat from the facility's exhaust air stream before
it is vented outside. Energy recovery from the laboratory's
exhaust should be considered when significant portions
of operating hours are at ambient temperature of 50°F
(10°C) and below. Another recoverable energy source
is provided by chiller/DX condensers. Water cooled
condensers can be piped to reject waste back into
the labs HVAC system to provide reheat capacity, to
augment run-around coil systems, and to dry regenerative
heat wheels. When properly designed, these energy
recovery systems can reduce installed HVAC system
capacity by one-half; reduce operating energy from
one-third to two-thirds, depending upon mode of operation;
and have life-cycle cost paybacks from immediate to
three years. The four major energy recovery systems
include run-around coil systems, regenerative heat
wheels, heat pipes, and fixed-plate exchangers
Plate heat exchangers
(recuperators)
A minimum effectiveness of 50% (based on sensible
energy transfer under balanced flow conditions).
Internal leakage < 1% (for units >0.2m3/second
rating)
Pressure drop <250 Pascal (Pa) NOTE: where pressure
drop data is not documented, the fan power consumption
must be consistent with a pressure drop within this
limit.
Thermal wheels
A minimum effectiveness of 70% (based on sensible
energy transfer under balanced flow conditions).
Internal leakage < 5%
Pressure drop <200 Pa
Run around coils
A minimum effectiveness of 45% (based on sensible
energy transfer under balanced flow conditions).
Pressure drop <100 Pa across each coil
Water side pressure drop < 25 kPa per coil
Heat pipes
Disadvantages of Energy
Recovery Ventilation.
Unlike air handling
units on unit ventilators, energy recovery systems
do not have the capability to provide sufficient outside
air for cooling overheated rooms. This can lead to
overheating, especially in the late spring and early
fall. Any building employing energy recovery ventilation
should have a by-pass sytem for ERV 's or operable
windows (or air conditioning) to provide cooling during
warm weather.
Energy recovery ventilation is not
a good choice for interior spaces unless those spaces
are air-conditioned.
A second area of concern involves the
fact that there is little standardization in the heat
recovery industry. Manufactures and products come
and go, and there is some concern that products specified
today may not have manufactures' support a few years
from now.
Heat exchangers to recover heat increase the pressure
drop of the air handling system, and increase the
power demand of the fans.
This is however typically only 5-10 % of the recovered
energy.
Air to Air
heat Recovery System Manufacturers
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