APC Fuel Cell Solution for Extended Run Time UPSDirector of Corporate Engineering Denmark, Klaus Moth,APC Denmark, DenmarkProjec Manager, Jacob Damgaard Schmidt, APC Denmark, Denmark

Abstract

Fuel cell technology is now a viable alternative to generators and extended-run batteries, allowing IT and facilitymanagers more flexibility in the specification, installation, and operation of critical facilities and avoidsenvironmental issues of other sources. This paper briefly explains the use of fuel cell technology in extended run-

time applications. A specific fuel cell based extended runtime system has been developed and the paper describesthe major system constituents. Substantial size reductions (in terms of footprint) have been achieved compared to

battery solutions.

1 Background

1.1 The Demand for Extended RunTime

Mission-critical applications like data centres are to-day mostly supported by a UPS-type of backup (Un-interruptible Power Supply). This system will sustainpower supply during grid outages and protect againstdisturbances on the supply line. Normally, such a sys-

tem offers a limited rmn-time in the range of minutes -i.e. enough to support a variety of strategies like

* Ride-through for short outages (that are mostfrequent)

* Time for a graceful and controlled shut-downof critical systems (where re-establishmentotherwise would take substantial resources)

* Time for re-configuring the application (likeshifting the most important services to re-

dundant sites).

Today, such strategies are in-sufficient for an increas-ing number of businesses. In addition to this growthin demand, the occurrence of outages is increasing inmany countries due to de-regulation of the energy

supply. The reason behind this is, that increased com-

petition and liberalization of the electricity market

ex, I

lb. 2

tends to reduce design margin from the grid and movee.g. the cost of high-availability-demand to customersthat need it.This increasing quality gap between supply and de-mand may be dealt with by so-called eXtended Run-time (XR) solutions that are capable of sustaining thecritical load for hours or even days.Practically, such solutions are still based on a UPS -

now fitted with an XR solution. Therefore, EcendedRun-time is often called an Extended Run Option thatis offered in addition to a standard UPS solution. Inmost cases, this XR option may be added to an exis t-ing UPS installation. Figure 1 outlines a few basicprinciples of offering extended run-time.

There are several ways of providing the extended run-time - see Fig. 1. The most common solution today isstill the use of a diesel generator.

1.2 Extended Run-Time Solutions

Table 1 outlines some typical technologies for XR.

Fig. 1. Different principles of offering extended run-time. The dashed line illustrates a so-called ramp-inof the diesel generator provided by the most advancedUPS systems.

Ema=l.a

UPS wthfout XR

UPS Wmt Dieselgenerator

UPS ~with ZRBaftery

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W."'I'lEllMillis

XR Solution Fuel Principle of usefor back-up

Diesel gen- Diesel oil Starts after preseterator duration of outage

Re-fuelling possi-ble during outage

XR batteries N/A - is charged Extension of thefrom the grid built-in runtime ca-

pacityMicro tur- Natural Gas, Same as for dieselbine Diesel oil, generator

Methanol (oneof these, only)

Fuel cells Hydrogen (can Same as for dieselbe made from generatorcracking naturalgas or other fo s-sil sources - orfrom bio gas orelectrolysis ofwater)

Table 1. Alternative technologies for extended run-time solutions.

This paper does not deal with continuous generationapproaches, where one may say that the grid supply isused as back up and the main power source is the on-site generator systemn

2 Fuel Cells

2.1 Basics

Basically, a fuel cell is a device that is capable of per-forming a controlled electrochemical reaction betweenHydrogen ions (protons) and Oxygen producing elec-tricity, water and heat. In principle, this is the reverseprocess of splitting water molecules into Hydrogenand Oxygen by the use of electrical energy (electroly-sis). The intrinsic characteristics that make fuel cellsattractive are

* Simple process that directly converts chemi-cal energy into electrical energy - this pro-vides the basis for a high energy conversionefficiency

* No-emissions-potential (waste products arewater and heat)

* Low complexity providing for low cost andhigh reliability

* Competitive energy density.

Despite such very promising intrinsic characteristics,there are substantial differences among various i-

plementations and their ability to reach out for the in-trinsic advantages. Presently, one of the most maturetechnologies is the PEM fuel cell. Although it exhibitssome lifetime issues, the present lifetime capabilities issuitable for back-up applications. Besides, the PEMtechnology fully complies with the demand for a fastcold start (a few seconds).

3 An Extended Runtime Solu-tion with Fuel Cells

This section describes the Fuel Cell Extended Run so-lution. The system has been developed for the APCInfrastruxure UPS concept and is intended for placinginside the data room.

Fig. 2. The Fuel Cell XR system (cooling rmdule notmounted).

3.1 System Description

The system consists of 1, 2 or 3 Fuel Cell Power Mod-ules to support 10 kW, 20 kW or 30 kW AC at the UPSoutput. Each Fuel Cell Power Module is connected toa DC/DC converter that converts the fuel cell outputvoltage to match the UPS battery bus.

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Fuel Cel Power DC/DC UPSModule Converter .(nfrastruXure)

.. ....

Fuel Cell Power DC,DC -19V OV +192VModule Converter

....................~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~...........................

Built-In Batteries

Fuel Cel Power DC/DCModule Converter

Fig. 3 Basic architecture of the extended run solu-tion.

The system fits a standard APC InfrastruXure suchthat extended runtime may be achieved without any

modifications to a standard UPS.A controller module comprises power supplies and a

controller handling the protocol among the fuel cellmodules and the UPS system. It also provides themeans for remote monitoring and data logging.

3.2 The Fuel Cell Power Module

The PEM Fuel Cell power module provides DC electn-cal power that covers the following power budget:

Efficiencyduringoutage Power Output(worst case) (kW)Worst Case kW

12,0

Con: l" 0,2

D.C/D ue %10,7

93% 10

.~ ~~~~ ..i....-0-00W .....--

A key parameter is a fast start-up time such that thefuel cells may cover the load after say some seconds.This start-up time should be compared to the runtimeprovided by the UPS built-in batteries (down toapprox. 7 minutes @ 30 kW). It is mandatory that thismaximum start-up time is known and guaranteed underany possible conditions. The worst case start-up timefor the applied fuel cell power modules is 18 seconds.In case of a failure in a specific module, this allows forsufficient time to implement the "site strategy", e.g.

* Repeated attempts to start a failed module* Starting redundant XR systems or modules* Reducing the the critical load* Graceful shutdown of server applications.

The Fuel Cell Power Modules applied exhibit the fol-lowing key characteristics:

raX-me--ter --i---i0 ---- Un ' ValueOutput voltage range V 37-57Maximum start-up time s =18

Maximum output power kW 13Efficiency Beginning-Of- % >47%

Life and 12 kW based onLHV of consumed fuelDimensions 19" rack mount

- 7u heightThe Fuel Cell Power Modules for this project are pro-vided by Hydrogenics Inc.

3.2 DC/DC Converter

A DC/DC converter was developed for the specificapplication. One of the key challenges of the DC/DCconverter design is that the input voltage reaches itsminimum value at the highest power level, imposing ahigh inlet current.

Several DC/DC converter modules may be paralleled atthe outlets.

3.2 Installation

The objective has been to derive a generic approachoffering a safe, fast and simple installation.The rack itself is vented continuously, creating a smallunder pressure that inhibits accumulation of hydro-gen.

The hydrogen storage uses pressurized bottles, in thiscase of each 10 mvn hydrogen at 200 bar. The storageshould be placed outdoor in order to allow for easyaccess when re-fuelling. The storage may be re-fuelledon-the-fly using two storage banks - providing inprinciple infinite runtime. A hydrogen bottle provides1.2 hour ofruntime at 10 kW critical load.The water produced by the fuel cell(s) is collected in a

container in the bottom of the rack, from where it ispumped to a water drain. The system produces ip-proximately 6 liters of water per hour at 10 kW criticalload.The waste heat produced by the fuel cells must be re-

moved from the system. This is done via a liquid cool-ing circuit. See section 3.4 for more details.The cathode exhaust is lead outside the room by a

duct. The exhaust consists of steam and air.The power cDnnection to the UPS is carried out byshort cables connected to the XR Battery inlet of theUPS.

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Input voltage range V 35-60Output voltage V ± 192Maximum output power @ kW 14minimum input voltageEfficiency ( full power and % >91%minimum input voltage _Dimensions 1 9 rack mount

3u height

3.3 Cooling Aspects

This section discusses different approaches regardingremoving heat from the system and away from the dataroom during an outage.

Power Total Wild Heat HeatOutput Heat Heat via via

Losses Ex- waterhaust cool-

ingkW kW kW kW kW10 15,3 2,0 2,4 10,9

There are several solutions to choose from, see tablebelow. This table outlines the utilization of the fuel cellfor serves and thus provides some guidelines for howto dimension the FC generator(s). E.g., 84% in the up-per row means that we need a Fuel Cell with the capac-ity of 1 1.9 kW to run servers using 10 kW.

Cooling approach UPS FCServer serverLoad load

1 - Electronic losses, only 100% 84%2 - UPS drives all heat out 49% 41%by air conditioning3 - Tap water or cold water 93% 78%reservoir4 - Dry cooler for FC and 69% 58%chiller for roomNotice: Based on COP=3 for chillers.

1) Disregards all cooling to demonstrate Fuel Cellutilization disregarding cooling

2) All heat is removed by air conditioning run by theUPS

3) All heat during an outage is eliminated by a coldstorage (cold water, ice, etc)

4) A dry cooler rejects the heat of the fuel cell and achiller cools the data room.

3.4 Reliability Aspects

A key driver of demand for extended runtime is thepace for decreased un-availability of the power supplyfor the critical applications. This solution supportsthis demand through

* Elimination of the automatic transfer switch(an important contribution to unavailabilitysince it is single-point-failure and cannot betested)

* Low complexity with very few moving partscompared to e.g. a combustion engine.

A Fuel Cell Power module has been cycled throughmore than 6.000 cold starts with no failures and nomeasurable degradation beyond the contribution fromnormal accumulated run-time.

3.5 Footprint Comparison

The footprint as function of the runtime has been cal-culated based on the following assumptions:Fuel Cell: 1 rack for 30 kW powerHydrogen storage: standard 50 liters bottles, 200 bar,23 cm diameter, vertically placed, 3 bottles per hourruntimeDiesel generator: data from [1]Battery XR solution: standard lead acid batteries (thefirst rack offers up to 20 minutes runtime @ 30 kW).

Gross Footprint[Square meters]

12,00 .10,008,00

6,004,00

o nre . ^B-:. '<-i- t; Z = - = , . ' : ., :. >..,....... .........N2,000,00

0 2 4 6 8 10 12 14Runtime [hours]

FC XR 30 kW - BatteryXR30 kW - Diesel30kW

Please note that the hydrogen storage will be placedoutdoor. The fuel cell solution is superior at any run-time below 12 hours. The footprint of the diesel solu-tion is smallest at runtimes beyond 12 hours, althoughthis is only relevant in cases where a diesel generatormay be applied.The fuel cell runtime is easily enhanced by addingmore hydrogen bottles to the storage. Finally, loweringthe load to partly loads will extend the runtime furtherdue to less power output and increased efficiency aswell.

4 Conclusion

.A, extended runtime solution has been developedbased on PEM fuel cells. The solution supports a ge-neric approach for safe and uncomplicated installation.Besides the intrinsic advantages of fuel cells, the solu-tion demonstrates substantial advantages over batterysolutions in terms of footprint.The system has been tested thoroughly, but obvi-ously the long term reliability remains to be proven.

5 AcknowledgementsThe author would like to thank the people from Hy-drogenics Inc, Toronto, for their agility and competentefforts throughout the project.

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6 Literature

[1] Generac diesel generator data sheet for typeSDO30, 2005.

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