Centrifugal Chiller Compressors with Magnetic Bearings and Variable Speed Control
Chillers: Centrifugal Compressors with Magnetic Bearings and Variable Speed Control vs. Standard Rotary Screw Chiller
Refrigerant compressors that use magnetic bearings in lieu of lubricated mechanical bearings. They feature an oil-free design, with an integral super-premium efficiency permanent magnet motor for speed control and soft starting capability.
Item ID: 109
Technical Advisory Group: 2009 HVAC TAG (#2)
Technical Advisory Group: 2015-1 Commercial HVAC TAG (#11)
Average TAG Rating: 2.95 out of 5
TAG Ranking Date: 03/10/2015
TAG Rating Commentary:
- There are only marginal increases in chiller efficiency. This is not where the big savings are.
- There is very little potential for this technology in BPA's territory.
- Widely available in a tremendous range of sizes from multiple OEMs. The program Q that I once worked on was how to build a chiller replacement program that would focus on the remaining stock of obsolete, low-efficiency, CFC-refrigerant chillers: modern units get rid of the ozone depletion, much of the GWP, and are almost twice as efficient.
- I'd like to see these in more HVAC applications, and I think the technology could be transferred to refrigeration compressor systems, with some research or potential cascade systems.
- I think it requires more testing
- Much improved efficiency for these type of chillers - heat pump systems eliminate the need for water cooling and water use.
Variable speed centrifugal chillers equipped with magnetic bearings save energy compared to conventional chillers by eliminating losses due to bearing friction. Part-load efficiency is improved through use of a variable speed drive and a compact design is achieved through operating at the ultra-high rotational speeds made possible through incorporating a super-premium efficiency permanent magnet motor into the design. Magnetic bearings also eliminate the maintenance costs associated with conventional metal bearings. Available compressors are also oil-free which further reduces maintenance requirements with the variable speed drive also allowing for soft start capability (soft-starting with a reduced amperage draw imposes a lighter load on backup generators, which may be of importance in some industrial sites) (From: FEMP Promising Technologies List).
Baseline Energy Use: 7.4 kWh per year per square foot
The 2009 Commercial Building Stock Assessment gives the actual electrical building energy use index (EUI) for various types of heating and cooling systems (Table D-EA5). Office buildings with electric heating and cooling have an EUI of 20.1 kWh/sf/year. Office buildings with no electric heating or cooling use only 8.2 kWh/sf/year, indicating that the combined HVAC heating and cooling energy use is 11.9 kWh/sf/year. For all commercial buildings, the corresponding numbers are 19.9 and 9.4 kWh/sf/year,respectively for a heating and cooling use of 10.5 kWh/sf-year.
Commercial buildings with electric cooling and with no electric heating have an electrical EUI of 16.8 kWh/sf-year (14.8 for office buildings). This indicates that the heating load for all categories of commercial buildings is about 3.1 kWh/sf-year (19.9-16.8) with a cooling load of about 7.4 kWh/sf-year (10.5-3.1). The corresponding electrical EUI for office buildings with electric cooling with no electrical heating is 14.8 kWh/sf-year which indicates a space heating load of 5.3 kWh/sf-year with a corresponding cooling load of 6.6 kWh/sf-year (11.9-5.3).
Since this technology can be applied to many types of buildings, a baseline commercial building and cooling energy use of 7.4 kWh/sf/year is assumed (NEEA, 12/21/2009).
Manufacturer's Energy Savings Claims:
Savings Range: From 10% to 50%
Best Estimate of Energy Savings:
"Typical" Savings: 30%
Low and High Energy Savings: 10% to 42%
Energy Savings Reliability: 3 - Limited Assessment
Testing of a 150-ton chiller screw compressor showed a full-load performance of 0.715 kW/ton. An equivalently sized Turbocor compressor performed at 0.645 kW/ton for a 9.8% improvement. When the Integrated Part-Load Value (IPLV) performance was measured, the conventional screw chiller performance was measured at 0.546 kW/ton while the Turbocore performance was improved to 0.371 kW/ton---for an energy savings of 32% in this example (WSU EEP, 2006). Other case studies showed energy savings of 20% at full-load and 55% at a load of 50%. An office building in Southern California replaced two 40-ton chillers with one 80-ton Turbocore unit and achieved an energy savings of 32% over a six-month operating period.
The new magnetic bearing/PM motor technology is more efficient under most circumstances. For an application that is operating at a nearly constant full load condition, the installation would not necessarily benefit from the variable speed, part load increase in efficiency. In their Promising Technologies Evaluation, FEMP states that magnetic bearing variable speed centrifugal chillers have been shown to reduce energy consumption by 42% compared to a standard rotary screw chiller. The magnitude of the savings is dependent upon demand profiles the type of unloading controls incorporated into the chiller design.
Energy Use of Emerging Technology:
5.2 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:
This technology could technically be used for conditioned space in virtually any commercial building, so we are using the total of the entire commercial building stock in the Northwest. The numbers are taken from preliminary updated numbers from the 2013 update to the Commercial Building Stock Assessment (CBSA) using the estimates for 2014 (before the update was completed -- from early January, 2014) multiplied times the percentage of commercial space that is conditioned based on the 2009 CBSA. This number is further multiplied by 74% to reflect space cooled by central systems using air-cooled or water-cooled chillers. Subtracted out is the percentage of space cooled by heat pumps and room air conditioners (Navigant Consulting, 2014 Appendix A, P-60).
While these Turbocore units are available in ranges from 60 to 90 tons, multiple units can be combined to meet higher cooling loads.
Commercial Floor Space Appropriate for Chillers with Magnetic Bearings and High-Speed Permanent Magnet Motors
Regional Technical Potential:
| || Total Floor space || || || % Conditioned || Applicable Space || |
% Cooled by Central AC and by Air
or Water Source Chillers
| || |
| Source || (NEEA, 2014) || || || || || || || |
| || 3,118,000,000 || || || 87.0% || 2,712,660,000 || 2,007,368,400 || || |
4.46 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
Emerging Technology Unit Cost (Equipment Only): $1.44
Emerging Technology Installation Cost (Labor, Disposal, Etc.): $0.00
Baseline Technology Unit Cost (Equipment Only): $0.00
The installed cost for retrofits should be in the range of $550 to $600 per ton of cooling. The cost for new chiller installation as well as energy savings and simple payback is presented in two tables available at the links below. As one ton will serve about 400 sf of commercial building space, an upgrading cost of $575/400 sf = $1.44 will be assumed.
Energy Ideas Clearinghouse PTR
Daikin McQuay Magnitude™ Chillers
Simple payback, new construction (years): 7.2
Simple payback, retrofit (years): 7.2
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.