4 FM quick reads on HVAC
1. Go Beyond Simple Payback To Justify Major HVAC Upgrades
Facility managers need not rely on simple payback to justify HVAC upgrades. A simple payback calculation is sometimes utilized to determine if an energy upgrade is justified. But the simple payback approach does not present the whole picture of the value of the upgrade.
The importance of a broader approach to justifying upgrades can be seen from a project conducted under the Commonwealth of Massachusetts' energy reduction program. The program aims to reduce energy consumption by 25 percent for all state-owned-and-operated facilities. The state used the simple payback method based only on energy savings (energy, rebates, and incentives) savings. The projects are expected to have a simple payback of 15 to 20 years or less to justify the investment.
A large state university evaluated under the program had identified a project with an energy savings of 21 percent and a simple payback of 19 years based upon energy consumption only. The university had to sell this project to its board and would have found it difficult with a simple payback of 19 years, but the university was also able to include the savings for deferred maintenance and deferred capital. The inclusion reduced the simple payback from 19 years to less than 9 years. (At the time of writing this piece, the contribution from utility company incentives and rebates for this campus was not included because a substantial amount of the design was not yet completed).
It's important to note that there were more than 150 energy conservation measures identified in this project, with simple paybacks ranging from 6 months to more than 50 years. When all of these were considered under one umbrella, the overall project had a simple payback that was in the range of the total system requirement. Bundling helped to move forward projects with long payback periods; this is carefully programmed so that the overall project is still able to maintain an acceptable payback period.
This brief came from Andy Jones, mechanical engineer/project manager at RMF Engineering.
Energy Recovery Systems Can Cut Energy Use Significantly
Energy recovery in buildings today is a true paradigm shift from traditional practice of 20-30 years ago, because the technology to accomplish it didn't exist. '"It is now commonplace to expect some type of energy recovery incorporated into the building's HVAC system," says Ron Holdaway, an engineer at Smith Seckman Reid. "Rather than throwing away the low grade energy generated in the building, technology today allows the energy to be recovered in efficient and practical ways." Especially for building owners who are large energy consumers, energy-recovery systems have the potential to cut conditioning energy use significantly.
Holdaway cited an airside heat recovery system that was recently designed for a 200,000 square hospital in the Memphis area. Hospitals require significant amounts of outside air to ensure proper control of microorganisms.
"By using heat-recovery systems, the air conditioning tonnage was reduced by over 200 tons," Holdaway notes. "The system also resulted improved indoor air quality by improved temperature and humidity control in the space."
Payback is anticipated to be four years or less.
Increasingly, these systems are required. For commercial buildings, airside and waterside heat recovery are required by ASHRAE 90.1-2010 and the International Energy Conservation Code (IECC). Holdaway notes that exhaust air energy recovery is required if the outside air exceeds a prescriptive quantity. The quantity of outside air is dependent on the climate zone of the building. Energy recovery system installation requires the aid of an engineer who can calculate the energy savings against current building energy use. Holdaway notes that it's essential to size the systems appropriately.
"Systems that are oversized will not perform well and result in unnecessary added costs. Systems that are undersized do not generate sufficient energy savings to pay back the initial investment," he says.
Questions to Answer Before Deciding on a Portable Cooling Solution
While facility managers may go years between purchases or leases of portable cooling systems, when they need one, it's often critical and urgent: The existing air conditioning system stops working on one of the hottest days of the year, or the computer equipment malfunctions due to inadequate cooling in the data center. Before signing a purchase or lease agreement for a new portable cooling system, facility managers will want to address the following questions:
• What's driving the need for a portable cooling system?
• What size area do you need to cool?
• What steps might reduce the size of the cooling unit needed?
• What is the energy efficiency rating of the equipment?
• Should I buy or rent?
• What steps can facilitate installation and maintenance?
Many facility managers evaluating new portable cooling systems will find that the technology has advanced significantly since the last time they were in the market. More powerful fans and more efficient compressors "have dramatically reduced the cost of essentially all cooling equipment, which has made its way into portable cooling technology," says Philip Winterland, project manager with Facility Engineering Associates. This reduces the amount of energy needed to cool a space.
In addition, the integration of indirect evaporative cooling (swamp coolers) into traditional systems can reduce the size of the compressor motor required, Winterland says. Again, this can save energy.
Because the need for a portable cooling system can occur quite rapidly, it helps to gain an understanding of the systems available when things are running smoothly. As the saying goes, it wasn't raining when Noah built the ark.
Energy Recovery Systems: Airside and Waterside
Energy recovery is an option for organizations using a direct exchange system that's increasingly being written into building codes and ASHRAE standards. There are two basic types: airside and waterside.
According to Ron Holdaway, an engineer at Smith Seckman Reid, airside energy recovery is the process of using the building's exhaust air to pre-condition the ventilation air for the building. The exhaust air passes through an energy recovery device such as a rotating heat wheel, a fixed plate heat exchanger, or a run-around coil. The energy from the exhaust air stream is transferred to or from the outside airside. In the summer, the temperature of the warmer, humid outside air is reduced before entering the air conditioning system, which reduces air conditioning system tonnage. In the winter, the cold outside air is warmed before heaters heat the air to maintain the space temperature.
A water-cooled system relies on chillers to cool the water, which is then distributed to air-handling units to condition the space. The heat from the air-handler coils is returned to the chiller where the head is returned to the air via fans or a cooling tower. Holdaway notes that waterside energy recovery systems capture some of the heat from the building before it is rejected. This recovered energy is often used to temper the building's heating hot water.
"Some form of water-side heat recovery is being used in most large buildings today," Holdaway says. "Best design practice today is to use dedicated heat recovery chillers to recover heat from building's return chilled water and produce heating and domestic hot water."
The results of such a set-up yield much higher efficiencies. If a typical high-efficiency gas boiler is 90 percent, efficiency, a dedicated heat recovery chiller is 300 percent efficient or greater to produce the same hot water, Holdaway notes.