MarCraft’s Energy Recovery Products provide an economical solution to maximizing ventilation without dramatically increasing the mechanical equipment cost, space requirements and operational costs.
What is Energy Recovery?
Energy Recovery uses exhaust air that contains heating or cooling energy to condition outside air. Utilizing this exhaust energy will lessen overall building consumption of energy, therefore reducing building operational costs as well as conserve natural resources..
Commercial buildings account for one-third of the nation’s total energy consumption as well as two-thirds of our country’s total electrical consumption. Utilizing MarCraft energy recovery products assists in greatly reducing this massive expenditure of energy by recovering up to 85 percent or more of exhausted energy.
While the design of energy recovery products can be custom manufactured to optimize any application or requirements, an energy recovery unit is generally defined by one of four major components found inside the ERU. The four components are:
- Plate-type Air-to-Air Heat Exchangers
- Rotary Energy Recovery Wheels
- Heat Pipes
- Run-Around Recovery Loop
PLATE AIR-TO-AIR HEAT EXCHANGERS
Plate Air-to-Air Heat Exchangers recover energy by crossing discarded exhaust air and ventilation (supply) air in side-by-side air streams with common recovery plates. The process “preconditions” the supply air thus requiring the primary conditioning media to do less work.
The Plate Air-to-Air Heat Exchanger offers one spectacular benefit others do not: There are no moving parts. Obviously, the absence of moving components results in lower maintenance costs and less unit failure!
Additionally, the Plate Air-to-Air Heat Exchanger only recovers sensible energy, causing the dry bulb temperature of the supply air to change while maintaining a constant dew point (wet bulb). This makes a Plate Air-to-Air Heat Exchanger an exceptionally low-maintenance energy recovery product.
Another consideration is the use of Heat Pipes, which also can be incorporated in energy recovery units. Heat Pipes require side-by-side air streams, similar to Energy Recovery Wheels and Plate Air-to-Air Heat Exchangers.
Heat Pipes are coils filled with a specific amount of refrigerant that naturally changes phases based on exhaust and supply temperatures, using vapor pressure to transmit energy. Unlike Energy Recovery Wheels, Heat Pipes recover only sensible energy. However, they rarely involve moving parts. Again, the lack of moving components results in lower maintenance costs and less unit failure. Sensible effectiveness of Heat Pipes is between 45 percent and 65 percent.
ROTARY ENERGY RECOVERY WHEELS –
‘TOTAL ENERGY RECOVERY UNITS’
Energy Recovery Wheel units retrieve a portion of exhausted energy by utilizing an enthalpy wheel that rotates between the supply and exhaust air streams. The distinct advantage of the Energy Recovery Wheel is that it can recover both sensible and latent energy.
Utilizing the latent energy can vastly increase the effectiveness of the wheel, especially in hot, humid environments. For instance, a 50,000 CFM energy recovery unit can have a total effectiveness of up to 85 percent, depending on design conditions. Partial loads are accounted for by varying the speed of the rotating wheel or by bypassing air.
One concern regarding the Energy Recovery Wheel is cross-contamination. This is averted by designing wheels to solely transfer moisture and not airborne contaminants. A purge can also be built into the wheel to wipe the wheel with fresh outside air, further reducing cross-contamination.
According to ASHRAE, the purge section on an enthalpy wheel reduces cross-contamination to less than 0.1 percent when properly applied.
RUN-AROUND RECOVERY LOOP
The job of Run-Around Loops is to circulate a liquid between two different air streams. By simply adding pumps and coils, this becomes a cost-effective energy recovery solution.
Unlike the other Energy Recovery devices, a Run-Around Loop can take advantage of air streams that are not directly next to one another. Run-Around Loops have limited moving parts and have no cross-contamination issues. However, due to the typical distance between the outdoor air unit and the Heat Recovery Unit, this type of system also requires onsite interconnecting piping.
A major benefit to this system is that, if properly designed, pre-heat coils can function as the energy discharge side of the loop in the outdoor air unit. These types of systems are typically controlled by varying water flow with a VFD-driven pump, or by using a three-way bypass valve. Sensible effectiveness is estimated between 55 percent and 65 percent.
Installing energy recovery can dramatically reduce the cost and demand of energy in many different applications. The criteria to consider when selecting the correct type of energy recovery unit (ERU) for your application are as follows:
- Equipment Space Requirements
- Cross Contamination Issues
- Location of Supply and Exhaust
One major consideration that should not be overlooked when selecting an energy recovery unit is leakage. The MarCraft energy recovery system standard design casing leak rate does not exceed one percent of design airflow at 150 percent of the system’s highest total static pressure. Selecting a MarCraft energy recovery unit ensures the customer that they not only have the very best casing, but also have further reduced cross-contamination and wasted energy due to leakage.
MARCRAFT’s team of experienced engineers is eager to work with end users, contractors and other engineers to solve the most unique HVAC challenges.