Hybrid Direct Expansion With Evaporative Pre-Cooling
Mechanical Cooling: Evaporative Pre-cooler vs. Direct Expansion Cooling
Hybrid cooling that couples conventional high-efficiency mechanical cooling with one or more evaporative cooling techniques to minimize compressor electricity demand and consumption.
Item ID: 59
Residential, Commercial, Other
HVAC--Other HVAC Systems
Technical Advisory Group: 2010 HVAC TAG (#3)
Average TAG Rating: 2.7 out of 5
TAG Ranking Date: 06/29/2010
Technical Advisory Group: 2009 HVAC TAG (#2)
Technical Advisory Group: 2014 Residential Building TAG (#10)
Average TAG Rating: 2.21 out of 5
TAG Ranking Date: 04/10/2014
TAG Rating Commentary:
1. I don't believe that the market saturation in our area for air conditioning is high enough for this measure to be of much benefit.
2. How effective are evaporative technologies in the NW?
3. Great technology, but increased maintenance requirements and freeze protection issues may severely limit the circumstances in which this type of equipment can be reliably deployed.
4. Cooling demand in the PNW is not high enough to justify this investment
Technical Advisory Group: 2015-1 Commercial HVAC TAG (#11)
Average TAG Rating: 2.56 out of 5
TAG Ranking Date: 03/10/2015
TAG Rating Commentary:
- Especially useful East side of cascades.
- The maintenance costs and limited PNW application, make this a low priority.
- A little study to see at what power cost this makes sense for what NW buildings in which climate zones. Fantastic in the hot-dry SW. Does it make sense in the Pac NW? Only in the less populated inland areas? I just don't know.
- Totally makes sense. Concerned about increase water consumption.
- Very good for hot dry climates
- Too expensive
- Assessment needs to account for North West climate.
This "off-the-shelf" hybrid cooling technology couples conventional high-efficiency mechanical cooling (DX) with one or more evaporative cooling techniques to minimize compressor electricity demand and consumption. It is not an "add-on" device. This technology focuses on rooftop packaged air conditioning equipment applications in climates with less than ~60% relative humidity in cooling mode, and combines indirect evaporative cooling with high-efficiency vapor compression. Each component can operate independently or in unison, based on ambient conditions and cooling demand. Hybrid cooling can use many different configurations and system logic; however, evaporative cooling is generally accomplished through an indirect method that cools sensibly without adding moisture to the supply air.
For the indirect method, air is passed over water coils to transfer heat from the air to the water. For the direct method, air is passed through a wet mesh, transferring heat from the air to the water. This method is cheaper and more energy-efficient but adds humidity to the conditioned air. Either method provides some, if not all, of the cooling needs, thereby saving compressor energy. Some models use both methods.
The UC Davis “Western Cooling Challenge,” operated by the UCD Western Cooling Efficiency Center, is a multiple-winner competition that recognizes all units that can reduce electrical demand and energy use by at least 40% compared to DOE 2010 standards. To date, two manufacturers,Coolerado and Trane, have met the challenge with commercially available equipment.
Savings depend on climate conditions, use of building, etc., but some applications on hot, dry locations have demonstrated up to 80% cooling energy savings.
Baseline Description: DX cooling w/reheat
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 is14.8 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 commercial buildings, a baseline cooling energy use of 7.4 kWh/sf/year is assumed (NEEA,12/21/2009).
Manufacturer's Energy Savings Claims:
"Typical" Savings: 70%
Savings Range: From 50% to 80%
Energy savings is dependent on cooling needs and climate; however, based on (Davis, 2006) , the Coolerado H80 claims savings of approximately 66% on peak HVAC electricity demand and 78% on annual cooling energy use compared to a conventional 2010 DOE Standards RTU. These savings were demonstrated in Sacramento, CA, which is a nearly ideal climate for this technology. Savings in the Northwest would have to be estimated and tested. The Sacramento Municipal Utility District (SMUD) Customer Advanced Technologies (CAT) program estimates 25% savings.
Best Estimate of Energy Savings:
"Typical" Savings: 25%
Low and High Energy Savings: 5% to 40%
Energy Savings Reliability: 3 - Limited Assessment
Please see the summary table from Reznor (Reznor, 2009) for a climatic analysis of the psychometrics for this technology:
Energy savings is dependent on cooling needs and climate; however, based on (Davis, 2006) , the Coolerado H80 claims savings of approximately 66% on peak HVAC electricity demand and 78% on annual cooling energy use compared to a conventional 2010 DOE Standards RTU. . These savings were demonstrated in Sacramento, CA, which is a nearly ideal climate for this technology. Savings in the Northwest would have to be estimated and tested. The Sacramento Municipal Utility District (SMUD) Customer Advanced Technologies (CAT) program estimates 25% savings. Savings in the Northwest could be significantly less. A savings of 25% of cooling system energy use will be assumed as we are limiting deployment of the technology to those areas most suitable for high performance.
Energy Use of Emerging Technology:
5.6 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 virtually any commercial building, so we begin our estimate of square footage by considering 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. It is likely, however, that the technology will be most suitable in spaces that both require air conditioning and are in a hotter and drier climate zone. Zone 2 (with 6,000 to 8,000 heating degree days (HDD) comprises much of eastern WA and OR along with much of Idaho). Figure #4 of the CBSA indicates that 12% of the commercial building floor space falls within Zone #2. The conditioned space suitable for this technology is thus estimated at: 0.12 x 2,640,946,000 = 316,913,520 sf.
The technical potential would increase significantly if demonstration projects verify that significant energy savings can be obtained in Western WA and OR.
Regional Technical Potential:
| || Total Commercial Floor space || % Conditioned || Conditioned space |
| Source, units || (NEEA, 2014) (s.f.) || (NEEA, 2009 App C) || (s.f.) |
| || 3,118,000,000 || 84.7% || 2,640,946,000 |
0.59 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
The incremental installed cost will vary by technology. Incremental cost for the Coolerado H80 at low volume production is estimated at $1,000 per installed nominal ton, compared to high efficiency conventional rooftop units.
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.
Savings depends on weather, use of building, etc. Studies have shown cooling energy reduction upwards of 80% in ideal conditions. The SMUD CAT program uses an estimated 25% savings. Savings in the Northwest will likely be significantly less. Cost effectiveness will also depend on the cost of the particular installation and electricity rates.
Hybrid cooling couples conventional direct expansion (DX) cooling with one or more evaporative cooling techniques to reduce compressor electricity demand and consumption. Control logic dictates that when the cooling load can be satisfied by evaporative cooling alone, the compressor is kept off. As weather conditions, cooling load and/or dehumidification needs dictate, the compressor is operated, but evaporative cooling will still be used to pre-cool the refrigerant, reducing the load even when the compressor is running.
The most well-known example of this is the Coolerado Cooler. An advanced ultra-cooler that uses a hybrid indirect evaporative cooling and refrigeration direct expansion (DX) system. Return air (RA) and outdoor air(OA) are brought into the unit and cooled by an indirect evaporative media. Between 43% and 46% of this air is used as an indirect evaporative cooling stream. The balance is then passed through a refrigerant evaporator coil and supplied to the space by a high-efficiency fan. The exhaust air from the evaporative process is generally cooler than the ambient air and is therefore used for the heat sink air flow going through the refrigerant condenser coil. OA and exhaust air (EA) flow rates are matched during testing. The RA and supply air (SA) flow rates are also equal, thus there is no make-up air (to the space) supplied by the unit. The mode of operation can be described as recirculation and ventilation air cooling with no makeup air. The combination of indirect evaporative cooling with efficient compressors can provide dramatic decreases in peak demand and energy use for cooling in hot-dryclimates. In addition, some of these units use strategies like dual stage compressors to allow the RTU to operate only a first stage of capacity when at partial load and engage the second stage as load increases. This feature, combined with the hybrid evabporative/compressor cooling technology can increase savings substantially.
There are two standard cooling practices: direct expansion (DX) and evaporative. Each of these products is appropriate for use in different temperature and humidity ranges.
A conventional DX cooling system uses a compressor to drive a refrigerant through a vapor-compression cycle. Heat is extracted from the conditioned air at an evaporator coil, heat is rejected to outdoor air at a condenser coil, and cooled air is distributed to a space with a blower. The energy-consuming elements in this system are the compressor, a supply-air blower to circulate cooled air, and the fan that draws air across the condenser coil. This product is appropriate where tight temperature and humidity control is desired. Some locations in Hawaii will use two DX circuits in series to control the humidity.
There are two types of conventional evaporative coolers, direct and indirect. A direct evaporative cooler cools outdoor air by evaporating water into that air, increasing its humidity and reducing its temperature, and then blowing that air directly into the conditioned space. An indirect evaporative cooler uses the wet, cool air to cool a second stream of air, thereby avoiding any addition of humidity to the conditioned space. For both indirect and direct systems, the only energy-consuming elements are the fan and a small water pump.
Different approaches to hybrid cooling vary in their status. Some manufactures are in the early stages of market introduction, others are constructing and testing prototype machines, while others are considering appropriate fundamental designs. Coolerado and Reznor have products on the market today. Reznor off-the-shelf products range from 75,000 to 400,000 Btu/hr, 450 to 7500 cfm, and can build larger when requested.
End User Drawbacks:
Hybrid evaporative with DX cooling must overcome several barriers, including:
• Contractor/engineer knowledge of product existence.
• First-cost competitiveness.
• Field-proven useful lifetime.
• Field-demonstrated energy savings in various applications.
• Climate- and application-specific design optimization.
• Local constraints relative to on-site water use.
• Familiarity and trust among architects, engineers, HVAC professionals, technicians, facility managers, utilities, and other stakeholders.
• Limited availability.
Coolerado offers a couple of sizes. Dual Cool is custom manufactured to fit many larger rooftop units (RTUs) from different manufacturers. Reznor has packaged models and sizes to fit the residential and commercial market, and a lot of the industrial market from 75,000 to 400,000 Btu/hr, 450 to 7500 cfm.
Operations and Maintenance Costs:
No information available.
This technology is too new to have a field-proven effective lifetime. As with other HVAC equipment, lifetime will depend on service conditions and the quality of preventive maintenance programs. The effective life of these systems will also be impacted by water quality and maintenance protocols; however, laboratory tests indicate that properly maintained systems should have lifetimes comparable to conventional systems.
The main two non-conventional alternatives that would compete with this technology are direct-indirect evaporative coolers, variable refrigerant flow, and ductless mini-split heat pump or air conditioning systems. In some situations – particularly in hot, humid climates – direct-indirect cooling alone may not be adequate to meet cooling loads.