Installation of Proton
Exchange Membrane Fuel Cells at Residences for Combined Heat and Power
|
Darrell
D. Massie, Ph.D., P.E. Associate Professor Dept Civil and Mechanical
Engineering US |
Daisie
D. Boettner, Ph.D. Associate Professor Dept Civil and Mechanical
Engineering US |
|
Cheryl A. Massie, LC President Massie+Massie Consulting
Engineers |
John H. Kang Dept Civil and Mechanical
Engineering US |
Summary
Three proton
exchange membrane fuel cell systems have been installed to provide electrical
power and waste heat for three separate residences. The 5 kW fuel cell systems continually
operate in a standby power configuration with waste heat used for domestic hot
water and space heating. The fuel cell
systems operate at steady state providing a preset level of power which is fed
into the residence and the utility grid.
During periods of utility power outage an automatic transfer switch
disconnects the residential power source from the grid, providing power from
the fuel cell system with battery.
Residential loads are prioritized during this time to accommodate the
preset level of power available from the fuel cell system. When grid power is reestablished, the
transfer switch automatically synchronizes the fuel cell system with the grid
and then reconnects the two. This paper
describes issues relating to installation of the fuel cell systems.
1. Introduction
The US Department of Defense (DoD) spends over $1
billion a year to provide heat and power to their buildings. Additionally, they require innovative power
solutions for mobile applications such as base camps, mobile equipment, and
ground and aerial vehicles. Given this,
the DoD is interested in the development of alternate power sources, and
supports research and testing to pioneer technologies associated with micro
power plants. The DoD currently supports
research in proton exchange member (PEM) fuel cells due to their high
efficiency, flexibility in size, low operating temperature, and low emissions.
In addition to broader funding for fuel cell
demonstrations at military facilities, recent funding has targeted PEM fuel
cells for residential applications. The
goals for this program are to assess fuel cells for providing power in support
of sustainable design and to study their viability as an alternative power
source to the DoD; to study the effect fuel cells have on the DoD’s ability to
construct, operate and maintain facilities; to assess installation and
operation issues associated with the use of PEM fuel cells; and to stimulate
growth in the fuel cell industry, Holcomb (2004).
This paper focuses on the issues associated with
the installation of three residential PEM fuel cell
systems located at a military base in
2. Fuel Cell
Configuration
The fuel cell systems
use natural gas as the fuel source.
Autothermal reforming of the natural gas provides hydrogen reformate for
the fuel cell reactions. The fuel cell
systems are rated at 5 kW power output with three user selected settings
of 2.5, 4 and 5 kW. A battery, contained
within the fuel cell unit, provides transient load following capability. An inverter converts the DC supplied
electricity to usable AC electricity for the residence. Since the military installation is centrally
billed and the electrical demand is always much greater than fuel cell provided
power, there is no need to operate using a load-following scheme. The fuel cells are configured to continually
operate as standby power. With this configuration, power is continually supplied in parallel
with grid-produced electricity. Any fuel
cell system generated power that is in excess to residence demand is fed back
into the grid. During periods of grid outage, an automatic transfer switch disconnects
the fuel cell system from the grid and the fuel cell system provides a preset
level of power to the residence. When
grid power is reestablished, the transfer switch automatically synchronizes
with the grid and then reconnects the fuel cell system.
The fuel cell system
waste heat recovery provides for domestic hot water and limited space
heating. Since the fuel cell systems are
installed as a retrofit, piping and installation costs for total space
heating would be prohibitive. Fuel cell
specifications are provided in Table 1.
Table 1 Fuel cell specifications.
|
Unit
size |
Base
Unit with integral skid: 84"L x 32"W x 68 1/4"H (excludes
22" exhaust stack) |
|
Installation
location |
Outdoor |
|
Electrical
configuration |
Grid
standby |
|
Power
output/setpoints |
2.5,
4 and 5 kW |
|
Data
collection and monitoring |
Remote
via phone line |
|
Output
voltage |
120
VAC @ 60Hz |
|
Certification |
Integrated
System CSA International Certified; Inverter UL Listed |
|
Power
quality |
IEEE
519 |
|
Emissions
(steady-state) |
NOx
< 1PPM |
|
Standard
operating conditions |
Temperature:
0-104oF Elevation:
0-750 Feet Noise<
65 dBa @ 1 meter |
|
Waste
heat utilization |
System
efficiency dependent on external cogeneration loop temperature and flow rate. |
|
Electric
only efficiency |
26%
@ 2.5kW 25%
@ 4.0kW 23.5%
@ 5kW |
|
Projected
overall efficiency |
50%
@ 2.5kW 55%
@ 4.0kW 50%
@ 5kW |
The system installed includes a wall-mounted,
customer interface panel that allows emergency shut-off of the fuel cell
system. The fuel cell manufacturer
provided instructions for emergency shut-off procedures. The customer interface panel
also shows the operating status of the fuel cell system, comparing the current
power setting to the actual power produced.
An alarm notifies the occupants when the battery drops below a set
threshold, when a power outage occurs, and when the residential power demand exceeds
the capability of the fuel cell system.
1. Installation
Issues
This section provides resident observations as the
fuel cells were installed. Since the
residents are engineers, their interest and knowledge of the technology are
most likely beyond that of a typical resident.
3.1 Siting
Several factors affected the ultimate
location of each fuel cell system in relationship to the exterior of the
residence. The reformer stack protruding
from the top of the system must be at least ten feet from the closest window by
governmental regulation. The
manufacturer placed the systems on temporary gravel foundations at all
locations.
The manufacturer desired to limit the
exterior piping distances between the fuel cell system and the residence. The piping requirements include the fuel cell
cooling water loop, the deionized water loop, electrical, control and natural
gas connections. Piping entry to all
three residences was made through a basement window, where the installer removed
one pane from the window and replaced it with a plywood board. All of the pipes were located above ground
and were routed through holes drilled into the plywood. The installer insulated the exterior cooling
water loop pipes and deionized water pipes with foam pipe sleeves and installed
a plywood cover to shield the pipes from open view.
Since these fuel cell systems are
scheduled to be removed after only one year, temporary measures were used. For a permanent installation, a concrete pad
in lieu of a gravel foundation is recommended.
Additionally, burying the pipes rather than above ground piping is
recommended.
3.2 Water
Supply Temperature
The
ideal setpoint temperature for domestic hot water is not entirely clear. The user-selected setpoint is typically a balance
between safety and water usage. ASHRAE
(1999) recommends water storage temperatures in the 60oC (140oF)
range so as to limit the potential for Legionelia pneumophila growth. Since Legionelia pneumophila bacteria
requires moisture for survival, water temperatures between 27-49oC
(80-120oF) promotes its growth, ASHRAE (1999). Ciesieiki et al. (1984) determined that
Legionelia pneumophila can colonize in hot water systems maintained at 49oC
(115°F) or lower.
Excessively
hot tap water supply is extremely dangerous and at temperatures above 46.1-49oC
(115-120oF) can in a short period of time result in serious or fatal
scald burn injuries. The degree of
injury is dependent upon skin sensitivity to heat and exposure time; children
and older adults being at highest risk of scald injury. Although water heater manufacturers often
recommend that installers set thermostats at 49oC (120oF),
the plumbing engineering community continues to recommend hot water systems be
designed with higher temperatures to reduce the threat of Legionelia
pneumophila growth.
One
method to help mitigate the balance between bacterial growth and risk of scald
injury is to maintain the domestic hot water at or above 60oC (140oF)
and then blend it with cold water such that tap water temperatures do not scald
occupants. However, thermostatic mixing
valves complying with ASSE 1017 are designed to control temperature from ±3.8oC
(±7oF), depending on the size when flowing at the required flow
rate. It should also be noted that ASSE
1017 has no test for compensation during pressure fluctuation. As such, the mixing valve needs to be located
at the hot water source to minimize pressure fluctuations between the hot and
cold water lines. To prevent bacteria
growth downstream of the blending valve, supervised periodic flushing of
fixture heads with 77oC (170°F) water is also recommended in
hospitals and health care facilities.
In
one of the residences, the pre-installed tap water temperature was measured at
52oC (125oF). The
adult residents manually controlled the tap temperature to avoid scald. The water temperature was maintained at this
temperature to accommodate dish washing and laundry, well short of the ASHRAE
1999 representative value of 60oC (140oF) for this
purpose.
After
installation of valves and pipes, the installed anti-scald
valve had a design range to allow water temperatures of 27-49oC
(80-120oF), lower than the pre-installation recorded
temperature. The actual maximum
temperature was measured at 47oC (116oF), slightly short
of the advertised range, but within manufacture’s tolerance. However, the
temperature was well short of pre-installation recorded temperature desired by
the occupant. Assuming that water heater
temperature could be maintained to 60oC by the fuel cell system and
given that ASSE 1017 recommends a high temperature source (8oC above
maximum mixing temperature), we recommend that any anti-scald valve have
a design range of 27-55oC (80-130oF) so that a full range
of household tasks may be performed. If
a future fuel cell system has an even higher water supply temperature, we
recommend that the upper range of an anti-scald valve be even higher.
3.3 Design of
Heat Recovery
There
are several methods for configuring fuel cell waste heat to recover domestic
hot water and space heating. One
consideration in the design is the requirement that domestic hot water often
requires a hotter temperature than space heating. This is because the water tank (sink) is at a
higher temperature, typically 60oC (140oF) than required
for a room, typically 21oC (70oF). Given that a PEM fuel cell rejects heat at 60oC,
the logical design is that heat recovery for hot water should be placed
upstream of space heating. Space heat
located upstream of hot water heating would result in an inability to maintain
60oC in a water tank. This
implies that during periods when fuel cell heat is used for domestic hot water
recovery, temperatures may drop (de-rating heat registers) below that required
for meaningful heat recovery.
A
parallel configuration might be considered, but this would add piping
complexity and it could be difficult to balance flow in pipe runs of different
lengths. At all three sites, domestic
hot water heat recovery hardware was located upstream of space heat.
3.4 Retrofit
Complexity
The
significant amount of piping (natural gas, water, deionized water) as well as
the routing of electrical wiring, makes retrofit a challenge. The basements in these residences are all unfinished
and thus exposed piping and conduit is acceptable. Installation to ensure that piping is not
exposed in finished rooms poses a greater challenge. Figures 1, 2, and 3 illustrate the extent of
piping and the large number of required connections. Since this is a retrofit project, the actual
piping configuration in each residence is different. Although the plumbing contractor’s
work appeared professional by every standard, the amount of piping required in
a limited amount of space, made the installation difficult.
Figure 1. Complex piping required near domestic hot
water tank in residence 1.
Figure 2. Complex piping required near domestic hot water tank in residence 2.
Figure 3. Complex piping required near domestic hot water tank in residence 3.
This
demonstration was the manufacturer’s first experience with combined heating and
power (CHP). Miscommunication about
piping for space heat resulted in a redesign of the piping flow pattern
supporting the heat exchangers. This
coupled with the very harsh winter of 2002-2003 posed installation
challenges. Large snowfalls inhibited
travel by installation crews and limited access to the fuel cell units that
were located outdoors. The fuel cells
have been heavily instrumented, however, delays in installing the fuel cells
have delayed operation and data collection in time for this paper.
3.5 Fire and
Safety Issues
Although fuel cell details are often found in the literature, few people understand
the details of how they operate or even what components comprise a fuel
cell system. Firefighters often are
among those who have not been introduced to fuel cell technology and lack an
understanding of equipment and chemicals that might be located within a fuel
cell unit.
For one installation,
tapping into the gas line to feed the fuel cell caused a gas leak that was not
noticed until construction workers departed.
When the occupant returned home for the evening, she noticed the leak. The local fire department was notified and
asked to assist. Firemen, being
cautious, were trying to be prepared for any possible hazard. As the occupant oriented the fire department
on the problem, the firemen revealed that they did not know how a fuel cell
worked and consequently did not know how to effectively fight a fire had one
been present.
As new technologies are
developed and integrated into residential use, consumers as well as public
safety officials need to understand the underlying operating principles. Until such time as fuel cell systems are in
wide residential use, appropriate measures should be incorporated into the fuel
cell installation. One suggestion is
labeling all piping with the content and flow direction to assist orientation
of the occupants and emergency personnel.
Additionally, manufacturer-produced pamphlets that describe the basic
operation and schematic of the fuel cell subsystems could help bridge the knowledge gap.
3.6 Reliability
Issues
The fuel cell
systems were placed on the ground in late December 2002. Installation of the piping and system
connection spanned a period of four months.
Prior to commissioning of the fuel cell systems, the manufacturer chose
to replace the fuel cell stacks in all three systems. Although the authors have no experience with
fuel cell reliability issues, replacement of the fuel cell stacks suggests
concern about performance and/or reliability of PEM fuel cell membranes that
have not been in a controlled environment prior to system start-up.
2.
Conclusions
Retrofit installations of
fuel cell systems pose practical challenges for residents and manufacturers
alike. Design choices, operating set
points, utilization of low temperature waste heat and safety issues require understanding
and careful design. Designs need to be
continually refined and fire fighting personnel need educational training for
potential hazards.
3. Acknowledgements
We would like to thank Dr.
Michael Binder and Frank Holcomb from the US Army Construction Engineering Research
Laboratory who funded and supported this demonstration, and the fuel cell
manufacturers for their continued patience and invaluable assistance in
configuring the fuel cells.
The views expressed in this
article are those of the authors and do not reflect the official policy or
position of the United States Military Academy, the Department of the Army, the
Department of Defense, or the US Government.
References
(1)
ASHRAE 1999. Ashrae Handbook: Heating, Ventilating, and
Air-Conditioning Applications, American Society of Heating, Refrigerating and
Air-Conditioning Engineers.
(2)
ASSE Standard #1017. 1998. Performance Requirements for Temperature Actuated Mixing
Valves for Hot Water Distribution Systems, American Society of Sanitary
Engineers.
(3) Ciesielski
(4) Holcomb, F.H. 2004. Results
of Residential Proton Exchange Membrane (PEM) Fuel Cell Demonstration at