Air Handling: Multiple Smaller Fans vs. a Single Large Fan
An air handler made up of an array of smaller fans that replaces a single large fan.
Item ID: 177
HVAC--Rooftop Units & Air Handling Units
Technical Advisory Group: 2009 HVAC TAG (#2)
Technical Advisory Group: 2015-1 Commercial HVAC TAG (#11)
Average TAG Rating: 2.5 out of 5
TAG Ranking Date: 03/10/2015
TAG Rating Commentary:
- Potentially useful to some customers, but not a large group.
- Good alternative to large fans with VFDs
- This technology is more suitable for new construction.
- It appears to have many potential benefits: possible lower costs and less space than big centrifugals, possibly easier to modulate, possibly quieter. Tries to use economies of manufacturing scale instead of economies of size.
- There are many applications for this system especially with good VAV controls. The savings depend on the building design. I think that HVAC systems that use VRF heat pumps will typically save more energy
FANWALL TECHNOLOGY was introduced by Huntair, Inc., in 2003, and is comprised of multiple small fans arranged in an array for an air handler (instead of one or two larger fans). This allows for smaller equipment to be used, which often saves energy, provides more precise air volume control, reduces noise, and provides multiple redundancy in case of equipment failure. It can also reduce down time and ease of maintenance. In addition, the fan array usually has a smaller footprint than a conventional single fan, often reducing needed floor space and making accessibility for maintenance easier. The lighter and smaller components can make installation in a retrofit situation easier to achieve. In most cases, however, the percentage energy savings is small – in the order of 2-5%.
Baseline Description: Multiple Direct Drive Fans
Baseline Energy Use: 2.8 kWh per year per square foot
Ventilation loads can be estimated from the 2009 NEEA Commercial Building Stock Assessment. Tables C-AF6 and C-AF8 provide the typical supply and return fan horsepower per 1,000 sf for all commercial buildings and for office space. For all commercial buildings, the total fan hp equates to1.08 hp or 0.8 kW/1000 sf. The input kW is obtained by multiplying by a load of 75% and then dividing by a motor efficiency of 0.9 (as hp is a motor output value) to obtain 0.66 kW/1000 sf. Multiply this value times the number of hours per year (79.3 hours/week x 52 weeks/year) to yield an annual energy use per square foot of 2.75 kWh/sf-year. For office space, the corresponding total connected supply and return fan connected hp is 0.72 hp total x 0.746 kW/hp x 0.75/0.9 or 0.45 input kW times 58.6 hours/week x 52 weeks per year/1000 equals 1.36 kWh/year. As this technology applies to custom air handling systems in larger buildings and custom application that are likely to have high air handling loads, use the 2.75 kWh/sf-year value for the baseline.
This technology can also be used in industrial applications. Semiconductor fabrication facilities are cited as an application (Huntair, Inc, 2005). The NEEA Microelectronics Initiative Market Progress Evaluation Report #2 (Peters, 2003) estimates semiconductor fab electric use to be 942 kWh/sf-year. It estimates that 46% of this is for chillers, air handlers, and exhaust fans (433). If we assume 20% of this is for air handlers that could be replaced by this technology, we get 87 kWh/sf-year. For the purposes of evaluation, the commercial baseline energy use is used to estimate technical potential, since the market for semiconductor fabrication facilities may be small.
Manufacturer's Energy Savings Claims:
"Typical" Savings: 8%
Savings Range: From 6% to 10%
Per Huntair, (Huntair, Inc, 2005), the savings are between 6% and 10% of the fan energy.
Best Estimate of Energy Savings:
"Typical" Savings: 5%
Low and High Energy Savings: 2% to 7%
Energy Savings Reliability: 4 - Extensive Assessment
The savings at each site will be based on many features, but, the most directly related to this concept is the drive losses that do not exist with direct drive fans. Typical losses for belt drive are about 5%.
Energy Use of Emerging Technology:
2.7 kWh per square foot per year
Energy Use of an Emerging Technology is based upon the following algorithm.
Baseline Energy Use - (Baseline Energy Use * Best Estimate of Energy Savings (either Typical savings OR the high range of savings.))
Potential number of units replaced by this technology:
These custom air handlers are a niche product - used for special applications with stringent requirements for unit size, reliability and noise generation. Typical applications include sports stadiums, semiconductor fabrication facilities and concert halls (Huntair, Inc, 2005). This product is for new construction and major renovation.
For commercial buildings, CBSA data ( Ecotope, Inc., 01/01/2014) includes projections of commercial building square footage that show an annual growth rate of approximately 1%. If we assume existing buildings have a 50 year life, then 2% of buildings will be replaced or have major renovations in a given year. Assuming the next 10 years of construction represents the new construction/major renovation potential results in 34% of existing commercial square footage (3,118,000,000, ) or 1,060,120,000 total square feet. Applying market shares from existing buildings, consider only conditioned square feet (85%) and Assembly (8%), or 72,088,160.
For semiconductor fabrication facilities, it is difficult to estimate future new construction potential. The NEEA Microelectronics Initiative Market Progress Evaluation Report (Peters, 2003) estimated 2,126,000 square feet of existing semiconductor fabs in the Pacific Northwest (~2003), but it also estimated there would be no new fabs constructed in the next few years and it estimated 80% of all new worldwide semiconductor fab construction in the near term would be in Asia and China. This could change and there may be potential for renovation of some of the existing square footage. Since the energy use in these facilities is large, the energy savings potential for just one application of FANWALL technology could be large. It is difficult to speculate what this might be, so industrial technical potential is not included in the technical potential estimate for this technology.
Regional Technical Potential:
0.01 TWh per year
Regional Technical Potential of an Emerging Technology is calculated as follows:
Baseline Energy Use * Estimate of Energy Savings (either Typical savings OR the high range of savings) * Technical Potential (potential number of units replaced by the Emerging Technology)
Installed first cost per: square foot
According to the manufacturer (Huntair, Inc, 2005) FANWALL costs are approximately $0.25 per cubic feet per minute of air delivery including installation. This is very close to the cost of a custom air handler utilizing a conventional plenum fan. Incremental costs for new construction are estimated to be minimal.
Simple payback, new construction (years): N/A
Simple payback, retrofit (years): N/A
Cost Effectiveness is calculated using baseline energy use, best estimate of typical energy savings, and first cost. It does not account for factors such as impacts on O&M costs (which could be significant if product life is greatly extended) or savings of non-electric fuels such as natural gas. Actual overall cost effectiveness could be significantly different based on these other factors.