Calstart/DARPA FY '96 — Final Report, April 10, 1998

Introduction

The mobile heating and air conditioning systems in use today on internal combustion vehicles do not lend themselves to efficient application in the EV market.  To date, numerous attempts have been made to try to adapt these systems by making rudimentary changes in one or two of the primary components. In a through analysis of these adapted systems, EPRI (Air Conditioning For Electric Vehicles, TR-102657) found them to be both under-powered and remarkably inefficient.  The most efficient unit tested averaged an EER (Energy Efficiency Ratio, BTU/hr output divided by watts input) of only 6.17.  This means that it required 30% more energy than would be expected of a common home window air conditioner.

While the air conditioning systems were proving problematic, the heating systems were not much better.  This was particularly true for purely electric vehicles which were relying on either electric "heat pump" systems or, fossil-fueled forced-air systems designed as supplemental heaters for trucks and boats.  A report issued by M.J. Bradley and Associates, following extensive heater testing by the Northeast Advanced Thermal Management Project found all but one heater to wholly inadequate to the task of properly heating Geo Metro in a Northeast winter climate.  None of the systems tested could be integrated into the air conditioning system and all systems tested were found to be overly complex and too large to easily install.

With an emerging EV market, the need for a powerful, efficient, purpose-built EV environmental control system is apparent.  Under a co-operative funding grant from DARPA (administered through Calstart), Glacier Bay began the work of applying the high-efficiency cooling technologies, which Glacier Bay had previously applied to the marine industry, to the development of a system that would fulfill this need.  The result was the Glacier Bay Environmental Control System (ECS) for Electric and Hybrid Vehicles.

Project Goals

The original goals of the project were to:

* Dramatically reduce energy consumption
Preliminary computer modeling and proof-of-concept testing indicated that the Glacier Bay Environmental Control System would operate at an EER of 11.22 under severe driving conditions and 15 under average conditions. At these levels of efficiency the Glacier Bay Environmental Control System for EVs would require 55% less energy than best EV air conditioning systems available. Under the same operating conditions, the most efficient vehicle air conditioning system identified in EPRI's investigation (Air Conditioning Systems for Electric Vehicles, EPRI-TR102657) averaged an EER of only 6.17.

* Reduce space requirement and lighter weight
Through the use of a small displacement, high-speed integrated compressor and high efficiency condenser/evaporator designs, a reduction of 50% in the total size and weight of the system was projected.

* Reduce maintenance and improved reliability
Leaking fittings as well as moisture and gas permeation of rubber hoses are the leading contributors to poor reliability of automobile air conditioning systems.  By designing the Glacier Bay ECS as the first 100% hermetically sealed vehicle environmental control system, the refrigerant leaks, moisture contamination, brush wear and belt adjustments which plague existing systems would be eliminated entirely.

* Increase heat output in cold climates
Based on research done by EVermont and others, it was determined that a minimum heater output of 5 kw (17,000 BTU/hr) would be required.  The fossil-fuel fired heater would be compatible with both propane and natural gas providing much lower emissions than that of diesel-fired heaters.

* Easily and inexpensively adapt to a wide range of voltage inputs
The system would be easily produced for operation from a wide range of input voltages thus effectively eliminating this restricting factor in capturing the low-volume production markets.

Accomplishments

Following is a point-by-point tally of the project's success in meeting the originally established goals:

* Dramatically reduce energy consumption
Glacier Bay's ECS achieved an EER of 11.36 under severe driving conditions and 15.80 under average conditions thus exceeding the original program goals by 5%.

* Reduce space requirement and lighter weight
The Glacier Bay ECS components total 60.82 lbs.  When compared with a typical combined heating and air conditioning system weight of 122.3 lbs, the ECS represents a weight reduction of 51.3% ⁽¹⁾ thus meeting the project goal.

* Reduce maintenance and improved reliability
The Glacier Bay ECS successfully achieved a 100% hermetically sealed design, thus meeting this goal.

* Increase heat output in cold climates
The Glacier Bay ECS achieved an output of 5.97 kw (20,361 BTU/hr) in a liquid circulating, fossil-fuel fired heater design thereby exceeding the original goals with a 19% over-capacity.  Additionally, the heater was demonstrated to be compatible with both propane and natural gas fuels.

* Easily and inexpensively adapt to a wide range of voltage inputs
In its final design, the Glacier Bay ECS is a system which can be easily produced for operation at any input voltage from 98 to 425 vdc.  Adaptation to various voltages is accomplished through with a wide input voltage motor controller.  To match any input voltage in the operating range requires only that the correct motor windings be used.  This ease of production customization meets the original goal.


Review of Work Performed

The broad purpose of the work in this project was to successfully adapt Glacier Bay high-efficiency DC technology to an environmental control system suitable for the electric vehicle market.  To apply this adapted technology in a complete fully-operational system, and to demonstrate that system in two sets of independently documented tests.  To this end, the work was divided into three task areas:

Task 1: Design and produce the major system components
Task 2: Design and produce installation-specific system components
Task 3: Performance testing

Specifically, the work performed in the individual task areas was:

Task 1: Design and produce the major system components
The major system components cover four specific items.

Task 3: Performance testing
The performance testing was divided into two phases and was conducted by Florida Solar Power Research Center and the University of California at Davis.

Performance Testing

Performance testing of the Glacier Bay ECS was conducted in two phases — Phase 1 for the air conditioning portion of the system and Phase 2 for the heating portion of the system.


Phase 1 — Cooling

The ECS air conditioning performance was tested on September 17, 1997 by Mr. Bill Young of Florida Solar Power Research Center (Cocoa, FL) under contract with EVermont.  The system was installed on a Solectria Force (Geo Metro) owned by EVermont.  The focus of the test was to measure the actual cooling performance in-situ in a high-solar load, high-humidity environment and to compare this performance to that of a factory-standard engine-driven air conditioning system.  The test was not intended to accurately quantify the output of the system (i.e. BTU/hr.) as these measurements had been previously made in a properly instrumented laboratory setting at the Glacier Bay facility.

The Test Circuit
The test was conducted at the Florida Solar Power Research Center which is situated in a non-congested rural area just outside Cocoa, Florida. The ECS equipped Solectria Force and an, otherwise identical, Geo Metro equipped with factory-installed engine-driven air conditioning system were left in full sun-soak in the parking lot all morning. In early afternoon, at maximum ambient air temperature, the two cars (each with one driver only) were driven out of the parking lot and followed each other through the surrounding streets. Driving speeds averaged approximately 45 mph and included several stop signs, stop lights and intersections.

Ambient Conditions
At the time of the test, the ambient conditions were:

Temperature — 91°F
Solar Radiation — 760 W/sq m
RH — 51%
Wind Speed — 4 m/s

Sensor Locations
In each vehicle, a total of ten Sensors were installed at the following locations:
(a) One at the outlet of the 2 main dashboard blower vents — total 2
(b) One at 31” above the seat (i.e. head position) in both the front and rear — total 4
(c) One at 14” above the seat (i.e. stomach position) in both the front and rear — total 4

Data Readings
Data was logged every two minutes.  The charts below give an average reading of the four sensors in each seat to provide a “Front seat” and “Rear Seat” temperature.  The two dash board readings were averaged to give the “Vent” temperature.

However, while both system performed well, there are some differences in performance characteristics that are notable. The following chart overlays the front seat temperature from vehicles for direct comparison:

In this chart it can be seen that the factory AC unit took longer to begin cooling the cabin. However, once it actually started to cool, the temperature quickly fell to reach (and slightly surpassed) that of the ECS.

A close examination of the test route reveals the cause of this cooling response and illustrates one of the advantages in a 100% electrically powered air conditioning system like the ECS.

Since the factory AC system is engine-driven, it is dependent on engine speed for its cooling power. For the first two minutes of the test, the test vehicles were exiting the parking lot and stuck behind a stopped school bus. With very little engine speed, the factory AC system accomplished very little cooling. On the other hand, being electrically driven, the ECS is independent of engine speed and was able to begin cooling immediately. The effect can also be clearly seen when one compares the vent temperatures for the two systems as in the chart below.

 

Negating the effect of voltage drop
One common problem found in previous electric air conditioning system test which were powered directly from the vehicle battery pack was a dramatic reduction in system capacity as the battery voltage falls.  This was a potential problem of special concern to Glacier Bay when developing the ECS control system.  For this reason, particular attention was paid to ensuring that system output remained as steady as possible through the discharge and regenerative braking cycle of the battery pack.  

A closer look at the battery voltage revealed that the input voltage fluctuated by almost 20% (30 volts) without substantial impact on the ECS system capacity.

Conclusion

The ECS air conditioning system performance matched, and even exceeded, that of the factory-installed engine driven air conditioning system.  The ECS maintained a comfortable cabin temperature at freeway speeds and under extreme heat loads.  While further tests are necessary, the test performed indicates that the ECS offers superior performance in heavy traffic conditions, where lower engine speed limit the A/C system capacity of the factory unit.

Though no direct measurements were taken during this test run, it is known from tests of similar engine-driven systems ⁽²⁾ and the bench-top efficiency tests of the ECS that this level of performance was achieved with only about 25% as much energy input.




Phase 2 — Heating

The ECS heating system test was performed on March 20, 1998 by Professor Andrew Frank of the Department of Mechanical Engineering at the University of California at Davis. Extensive previous testing had been already been conducted to determine the heating requirement of the Solectria Force test vehicle ⁽³⁾.  With the heating requirement of the car so well established, the intent of the U.C. Davis testing was to quantify the heat output and emissions of the Glacier Bay ECS system. The system was tested using natural gas fuel.

Test Protocol
U.C. Davis ran two separate tests for the ECS heating system. In the first test, a positive displacement water pump was used to circulate a constant, known mass flow of water through the heating unit.  Thermocouples recorded the Delta T between the incoming and outgoing water to determine the rise.  From this the heat output could be determined.  The purpose of the second test was to determine the emissions during steady state operation.  For this test the heater was connected to a finned coil air heat exchanger so that a stable steady-state condition could be achieved at normal operating temperatures.  The heater was activated and the discharged exhaust gas analyzed by a 5-gas emissions analyzer.

Test Result — Capacity
The following capacity was recorded for the Glacier Bay ECS heating system in steady-state operation:

Mass flow rate: 1,454.4 lbm/hr
Delta T: 14°F
Heating Capacity: 5.97 kw (20,361 BTU/hr)

Test Result — Emissions
The following emissions were recorded for the Glacier Bay ECS heating system in steady-state operation:

Nitrous Oxides (NOx): 24 ppm
Carbon Monoxide (CO): 0.12%
Hydrocarbons (HC): 3 ppm
Carbon Dioxide (CO₂): 6.1%

For comparative purposes, the tested emissions of a common competitive heating system are shown below ⁽⁴⁾:

Brand: Webasto
Fuel: Diesel/Kerosene
Nitrous Oxides (NOx): 200 ppm
Carbon Monoxide (CO): 0.2%
Hydrocarbons (HC): 100 ppm
Carbon Dioxide (CO₂): 10.5%

Conclusion

The Glacier Bay ECS heating system exceeds the performance goals set forth at the time of the project proposal.  With a capacity of over 20,000BTU/hr it has higher capacity than any auxiliary heating system tested by the Northeast Advanced Thermal Management Technology Project.  In fact, it matches that of water-circulating heaters in modern combustion engine cars.  As such, the heater would provide complete passenger comfort at temperatures of -25°F in any automobile or cargo van while retaining sufficient capacity for de-fogging all windows.  With its full heat output “instantly available”, the Glacier Bay ECS heater provides a distinct advantage over the engine-coolant heaters of today's gasoline cars.


1. Typical system weights were obtained from the average of all air conditioning systems tested by Arthur D. Little [EPRI-TR-102657s] and heating systems tested by the Northeast Advanced Thermal Management Project.
2. Air Conditioning System for Electric Vehicles, Arthur D. Little, Inc. # EPRI TR-102657s.
3. Northeast Advanced Thermal Management Project, M.J. Bradley and Associates.
4. Northeast Advanced Thermal Management Technology Project, M.J. Bradley and Associates. Of five heaters tested only the Webasto (shown) and one Espar were capable of properly heating the vehicle. The Webasto had the lowest emissions of the two.



For additional information on the Glacier Bay/DARPA ECS development project and system performance see: