Confidential Global Cooling Inc. Page 1 June 2013 

## FLAMMABILITY RISK	ASSESSMENT	OF	R

- 170	(ETHANE)	FOR	USE	IN VERY

- LOW
TEMPERATURE	FREEZER	THERMOSIPHON

SUBMITTED	BY:	GLOBAL	COOOLING	INC.,	6000	POSTON	RD.,	ATHENS,	OH	45701

JUNE	2013Confidential Global Cooling Inc. Page 2 June 2013 

### Table	of	Contents
1 G LOSSARY	OF 

### T ERMS AND 

### A CRONYMS


### ................................ ................................ ............................ 3

2 S UMMARY


### ................................ ................................ ................................ ................................ .......... 6

3 B ACKGROUND


### ................................ ................................ ................................ ................................ ... 7
3.1 Introduction

................................ ................................ ................................ ................................ ......... 7
3.2 VLT	Freezer	Study	Model

................................ ................................ ................................ ................. 9
3.3 Use	Profile	of	VLT	Freezers

................................ ................................ ................................ .......... 11
3.4 Data	References

................................ ................................ ................................ ................................ 12



### 4 D ETAILED 

### D ESCRIPTION	OF	THE 

### P RODUCT


### ................................ ................................ ................ 12
4.1 The	Stirling	Engine

................................ ................................ ................................ .......................... 12
4.2 The	Thermosiphon

................................ ................................ ................................ .......................... 13
4.3 Heat	Rejection

................................ ................................ ................................ ................................ ... 14
4.4 Electronic	Components

................................ ................................ ................................ .................. 14



### 5 G AS 

### L EAKAGE 

### E VENTS


### ................................ ................................ ................................ ................... 17
5.1 Manufacturing	Site

................................ ................................ ................................ .......................... 17
5.2 Servicing	Site

................................ ................................ ................................ ................................ ..... 17
5.3 Non

- Conforming	Leaks

................................ ................................ ................................ .................. 18



### 6 R ISK 

### A SSESSMENT


### ................................ ................................ ................................ ......................... 19
6.1 Introduction

................................ ................................ ................................ ................................ ...... 19
6.2 Probability	of	Leaks

................................ ................................ ................................ ........................ 23
6.3 Failure	Rate	Estimates

................................ ................................ ................................ ................... 26
6.4 Fault	Tree	Analysis

................................ ................................ ................................ .......................... 28



### 7 R ISK 

### M ITIGATION


### ................................ ................................ ................................ .......................... 29

8 D ISPOSAL 

### I SSUES


### ................................ ................................ ................................ ........................... 30

9 B IBLIOGRAPHY


### ................................ ................................ ................................ ............................... 30Confidential Global Cooling Inc. Page 3 June 2013 

### 1 G LOSSARY	OF 

### T ERMS	AND 

### A CRONYMS

Absolute	 risk :	 the	 quantitative expression	 of	 risk	 due	 to	 a	 specific	 cause	 in	 terms	 of	 both impact	and	probability.
AC :	Alternating	current. Accident	 sequence :	 a	 specific	 unplanned	 event	 or	 sequence	 of	 events	 with	 a	 directly attributable	undesired	consequence.
Acute	hazard :	the	potential for	injury	or	damage	resulting	from	an	instantaneous	or	relatively short	duration	exposure	to	the	effects	of	an	undesirable	event.
ADL :	Arthur	D.	Little,	Inc.
AICC :	adiabatic,	isochoric,	complete	combustion.
ASHRAE :	American	Society	of	Heating, Refrigeration	and	Air

- conditioning	Engineers
Baffle :	a	surface	used	for	deflecting	fluids,	usually	in	the	form	of	a	plate	or	wall.
Cabinet	 heater :	 an	 element	 embedded	 behind	 the	 thermal	 breaker	 (or	 mullion)	 for	 the purpose	of	providing	heat	to	the	freezer gasket	in	order	to	prevent	condensation	or	sweating.
CFM :	Cubic	foot	per	minute,	a	rating	typically	used	for	fans. Consequence :	the	direct	result	of	a	hazardous	event.
DC :	Direct	current. Deflagration :	 Propagation	 of	 a	 combustion	 zone	 at	 a	 velocity	 that	 is less	 than	 the	 speed	 of
sound	in	the	unreacted	medium. Episodic	event :	an	event	of	limited	duration,	usually	associated	with	an	accident. Equivalence	Ratio :	ratio	of	the	fuel

- to

- oxidizer	r atio	to	the	stoichiometric	fuel

- to

- oxidizer	ratio.
Event :	a	particul ar	occurrence,	sometimes	referring	 to	one	or	more	specific	steps	in	a	 failure sequence	leading	to	an	accident.
Fault	 tree :	 a	logic	 diagram	illustrating	 a	 ‘top

- down’	 chain	 of	 events	 showing	 a	 ‘top

- event’	 of interest	and	all	of	the	significant	event	sequence s	and	combinations	of	failures	that	can	lead	to
it.
Fill

- tube :	a	small	diameter	tube	where	a	gas	charge	is	entered	into	the	thermosiphon.	The	fill

tube	is	pinched	off	to	make	a	gas

- tight	seal	and	to	retain	the	charge. Flash	point :	the	temperature	of flammable	material	at	which	there	is	sufficient	vaporization	to support	combustion	of	the	material.
Fluid :	gas,	vapor	or	liquid.
Hazard :	 a	 chemical	 or	 physical	 condition	 that	 has	 the	 potential	 for	 causing	 damage,	 injury, fatality	or	other	type	of	harm	or	l oss.Confidential Global Cooling Inc. Page 4 June 2013 Hazard	 analysis :	 the	 identification	 and	 classification	 of	 hazardous	 events,	 which	 may sometimes	be	accompanied	by	the	determination	of	the	probabilities	of	their	occurrence	and	/ or	their	consequences.
Hazard	identification :	a	process	of	design	and	op erations	review	with	a	purpose	of	recognizing and	noting	significant	hazards	to	people	and	property.
Hazard	models :	mathematical	relationships	that	describe	the	physics	and	chemistry	of	hazard phenomena. Hazard	 zone	 (or	impact	 area) :	 the	 zone	 or	 region	 whe re	 hazard	impact	 has	 the	 potential	 to

occur. Impact :	 the	 ultimate	 potential	 result	 of	 a	 hazardous	 event,	 expressed,	 depending	 on	 the particular	 application,	 in	 terms	 of	 injuries,	 fatalities,	 environmental	 or	 property	 damage, business	interruption,	etc. Imp act	criteria :	 values	 of	appropriate	physical	parameters	 that	are	used	in	conjunction	with hazard	models	to	define	hazard	zones	or	impact	areas.
K

G :	the	deflagration	index,	measured	in	bar

- m/s.	A	constant	that	defines	the	maximum	rate	of pressure	rise	with time 

### d p d t 

# ( )

m a x of	a	deflagration	in	a	volume V ,	according	to	the	equation:



### K G 

### = d p d t 

# ( )

m a x 

### ⋅ V 3

Likelihood :	a	measure	of	the	expected	frequency	of	an	event	occurring.
MIE :	minimum	ignition	energy.	A	measure	of	the	least	energy	required	to ignite	a	combustible mixture.	Hydrocarbon	refrigerants	all	have	a	MIE	of	around	0.25 m J (Kunz	1998)

. NFPA :	National	Fire	Protection	Association.
Relative	risk :	the	expression	of	risk	in	terms	of	how	it	compares	to	another	risk. Refrigerant :	the	fluid	used	for	heat	transfer	in	a	refrigerating	system.
Risk :	the	potential	for	realizing	undesired	impacts	as	a	result	of	an	event,	facility	operation,	or other	activity.
Risk	 assessment :	 the	 methodical	 estimation	 and	 evaluation	 of quantitative	 or	 qualitative
measures	of	risk.
Risk	 evaluation :	 the	 assessment	 of	 risk,	 coupled	 with	 an	 appraisal	 of	 the	 significance	 of	 the
results

. Risk	management :	 the	 systematic	 control	 of	 hazards	 via	evaluations,	 decisions	and	activities relating	to	ri sk	acceptability,	risk	mitigation	and	the	effectiveness	of	risk	assessment. Risk	 mitigation :	 the	 implementation	 of	 appropriate	 measures	 for	 reducing,	 eliminating	 or transferring	risk.Confidential Global Cooling Inc. Page 5 June 2013 Risk	reduction :	the	introduction	of	modifications	to	an	existing	design, facility	or	activity	that tend	to	reduce	either	the	probability	or	potential	impact	of	a	hazardous	event.
RTD :	Resistance	temperature	device	usually	used	for	measuring	temperature.
Societal	risk :	a	measure	of	risk	where	the	impact	relates	to	society	in	ge neral	rather	than	to	an
individual. Stirling	engine :	a	 closed

- cycle	 heat	engine	 that	is	 capable	 of	 being	 used	as	a	 heat	 pump	 or	a power	producer.	In	the	application	discussed	in	this	report,	the	Stirling	engine	is	always	used as	a	heat	pump.	It	pumps	heat from	the	cabinet	to	the	immediate	environment	surrounding	the cabinet.	The	Stirling	engines	used	in	VLT	freezers	are hermetic	and	are charged	with	helium.
TEWI :	Total	Equivalent	Warming	 Impact.	A	calculation	 that	determines	 the	equivalent	global warming	ov er	a	fixed	period,	usually	10	years,	of	the	refrigerant	and	use	energy	of	a	freezer.
Thermal	breaker :	A	flat	surface	or	flange	separating	the	outside	surface	of	the	cabinet	from	the interior	surface.	It	is	typically	manufactured	from	a	low	thermally	conduc ting	material. Thermosiphon :	 a	 device	 for	 transferring	 thermal	 energy	 by	 the	 use	 of	 buoyancy	 or gravitational	 effects.	 In	 this	 case,	 all	 reference	 is	 made	 to	 a	 two

- phase	 thermosiphon employing	 a	 refrigerant	where	 the	 heat	is	 rejected	 by	 c ondensation	 and heat	is	 accepted	 by evaporation	or	boiling.
UL :	the	Underwriters	Laboratories	Inc. Uncertainty :	a	reflection	of	the	accuracy	and	/	or	precision	of	an	estimate.
VLT :	Very	low	temperatures	usually	below

- 70°C.
VLT freezer : a	 freezer	 for	 storage	 of items	 at	 V LTs,	 usually	 employed	 in	 biosciences, pharmaceutical	 and	 bio

- storage industries

. Also	 know	 as	 a n ultra

- low	 temperature	 or	 ULT
freezer.Confidential Global Cooling Inc. Page 6 June 2013 

### 2 S UMMARY

In	 order	 to	 move	 away	 from	 ozon e	 depleting	 chemicals,	 very	 low	 temperature	 freezer manufacturers	 have	 been	 emp loying	 refrigerants	 such	 as	 508B.	 Unfortunately,	 these refrigerants	 have	 been	 identified	 with	 extremely	 high	 global	 warming	 potentials.	 An
alternative	 to	 508B	 is	 R

- 170	 (ethane),	 which	 is	 known	 to	 have	 minimal	 impact	 on	 global warming.	However,	R

- 170	is	fla mmable	and	therefore	its	potential	use	in	this	application	must
be evaluated	in	terms	of	safety	during	freezer	manufacture,	shipping	and	use.
We	 have	 found	 that	 the	main	 risk	is	 a	 fire	 or	 explosion	inside	 the	machine	 compartment	 at initial	powering	of	the VLT	freezer.	We	believe	that	this	event	could	occur	because	shipping	or transportation	 stresses	 are	 the	 most	 severe	 and	 that	 they	 could	 damage	 the	 thermosiphon tubing	resulting	in	a catastrophic	leak	of	R

- 170.	The	risk	of	such	a	scenario	requires	the	leak to occur	in	the	last	30	minutes	of	transportation,	for	both	fans	to	not	work	at	the	switch	on	event and	for	an	ignition	source	to	be	present.	We	calculate	that	the	frequency	of	such	a	combination
of	events	to	be	2.4	x	10

- 1 1 /yr.

This	risk	assessment	is based	on a	number	of	sources	including data	presented	by	Arthur	D. Little	in	their	report	‘ Risk	Assessment	of	Flammable	Refrigerants	for	Use	in	Home	Appliances’ 1 and	other	data	collected	by	Unilever	in	their	risk	assessment	for	the	use	of	R

- 290 in	ice	crea m cabinets .	 In	addition ,	Global	Cooling	has	al so	retained UL	 for	evaluating	 the	safety	of Stirling engine	cooled	VLT	freezers	employing	thermosiphons	charged	with	R

- 170.
As	part	of	the	risk	assessment,	we	characterized	R

- 170	by	comparing	it	to	other	hydroc arbon refrigerants	 already	 approved	 for	 household	 refrigerators	 and	 commercial	 applications.	 We are	asking	the	EPA	to	approve	the	use of	up to	100g	of	R

- 170	for	use	in	VLT	freezers.

1 Arthur	 D.	 Little,	 Risk	 Assessment	 of	 Flammable	 Refrigerants	 for	 Use	 in	 Home	 Appliances,	 September	 10, 1991.Confidential Global Cooling Inc. Page 7 June 2013 

### 3 B ACKGROUND



### 3.1 Introduction

Glob al	Cooling	Inc.	manufactures Stirling	engine	cooled	VLT	freezer s

. The	Stirling	refrigeration system	 (consisting	 of	 the	 Stirling	 engine	 and	 thermosiphon) installed	 in a VLT	 freezer s	 is
shown in	 Fig. 1.	 The	 Stirling	 engine	 employs	 h elium	 gas	 as	 its	 working	 medium.	 Thermal transport	fro m	the	interior	of the	freezer	is	accomplished	by	the thermosiph on	that	contains	a refrigerant,	currently	R

- 508B.

Fig.	1 Main	Components	of VLT	Freezer with	Stirling	Refrigeration	System

Recently, a	number	of	enterprises	and	concerns	have	lobbied	for	na tural	refrigerants	owing	to their	better	fit	with	sustainability	objectives (ASHRAE	2011)

. Global	Cooling	In c.	has therefore
conducted a	 sustainability	 evaluation on	 a	 27.5 cu.	 ft. freezer	 where	 the	 thermosiphon refrigerant	 has b een	 replaced	 with	 the	 hydrocarbon	 R

- 170	 commonly	 known	 as	 ethane (Berchowitz	 and	 Kwon	 2012) .	 	 The	 tests	 were	 conducted	 with 100g	 of	 R

- 170	 versus	 the original	charge	of 200g	of	R

- 508B. Aside	from	the	lower	refrigerant	charge an d	zero	ODP 2 ,	the global	warming	potential	of R

- 170	is	5.5	(GWP 100 )	versus 13,396	(GWP 100 ) 3 for	R

- 508B

.
Two baseline	cascade	system s	were included	in	the	study,	one	with	blowing	agent	HFC

- 245fa and	 the	 other	with	 cyclopentane. The	 cascade	 system	is the	 current	 benchmark	 VLT	 freezer system and	the	use	of	cyclopentane	represents	units	sold	in	the	US	with	lowest	TEWI

. Owing mainly	to	low	use	energy,	the	Stirling	has	a	substantial ly lower	TEWI	grade	than	any	cascade system. Fig.	2	shows	a	comparison	of the	Stirling	VLT freezer a gainst	the	baseline	cascade	VLT

2 Ozone	Depletion	Potential
3 This	is	a	measure	of	global	warming	potential	over	a	period	of	100	years	compared	to	CO 2 .	CO 2 =	1	(GWP 100 )Confidential Global Cooling Inc. Page 8 June 2013 freezers .	 A	 typical	 household	 refrigerator	 is	 included	 for	 reference .	 Each	 displacement	 of	 a cascade	VLT	 freezer	by	a	similar	sized	Stirling	VLT	has	the	potential	of	saving	the	equivalent
TEWI	of ni ne household	freezers. In	addition to	the	TEWI	advantage ,	we found	no	substantial
differe nce	in	performance	when	using R

- 170 against	R

- 508B and	therefore decided	that a	full evaluation	of	the	potential	use and	safety	concerns of	R

- 170	was warranted

.

Fig.	2 Estimated	TEWI	for	Cascade,	Cascade	with	Cyclo pentane	Blowing	Agent	and	Stirling

Since	R

- 170	is	flammab le, the	consequences	of	this	had	to	be	fully	investigated	so	that	proper handling,	 transport	and	 use	 procedures	 could	 be	identified. The	 flammability	issue	 has	 been the	major	area	of	concern	and	our	risk	assessment	is	largely	about	this	item.	Other	aspects	of safety	 are,	 of	 course,	 also	 studied	 but	 they	 do	 not	 represent	 any	 significant	 issues	 not ordinarily	handled	by	procedures	alread y	adopted	for	the	safe	use	R

- 508B. Table	1	compares some	 pertinent	 properties	 of	 R

- 508B , R

- 170 , R

- 290	 (propane) and	 R

- 441A .	 R

- 170	 falls	 into safety	 group	 A3 (ANSI/ASHRAE	 2010) compared	 to	 A1	 for	 R

- 508B. R

- 290	 and	 R

- 441A, refrigerants	approved	by	EPA/SNAP,	are	both	in	safety	group	A3	and	are therefore subject	to maximum	 charge	 quantities. R

- 170	is	 very	 similar	 from	a	 safety	 standpoint	 to	R

- 290	and R

441A	and	VLT	freezers	are	also	similar	to	the	application s already approved by	SNAP for	use for	 these	 refrigerants.	 Therefore	 data	 collected	 and	 studied	 under	 risk	 evaluation	 for	 R

- 290
and	R

- 441A	will	be	pertinent	to	this	study. Where	use	differences	occur	they	will	be	identified and	appropriate	considerations	w ill	be	introduced. 0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00

CASCADE CASCADE (CYCLOPENTANE) STIRLING HOUSEHOLD FRIDGE (US) TEWI [tonnes CO2]Confidential Global Cooling Inc. Page 9 June 2013 Table	1	Phys ical	Properties	of	R

- 508B, R

- 170 , R

- 290 and	R

- 441A

Refrigerant R

- 508B R

- 170 R

- 290 R

- 441A

Common	or	Trade Name Suva	95 (DuPont) Ethane Propane HCR	188	C 1

Chemical	Formulae CHF3/CF3CF3 C2H6 C3H8 Blend	Ethane , Propane, Isobutene and	n

- Butane Molecular	Weight 95.39 30.07 44.1 48.23
Boiling	Point	(1	atm)	[°C]

- 88.27

- 88.7

- 42

- 42
Freezing	Point	[°C] Not	known

- 183.3

- 188

- 188
Critical	Temperature	[°C] 14.0 32.2 96.7 117.3

Critical	Pressure (abs) [MPa] 3.926 4.8839 4.25 4.3
Flammable	Limits	in	Air [%] (Lower	to	Upper) N one 3	to	12.4% 2	to	11 % (Kaufeld	2012) 2	to	11 %

Minimum	Ignition	Energy	[mJ] Not	applicable 0.285 0.25 Estimate	similar	to Propane *
Auto

- ignition	temperature	[°C] N one 515 470 450 Heat	of	Combustion	[MJ/kg] (Higher	Heating	Value) N/A 51.9 50.35 Probably	similar	to Propane Ozone	Depletion	Potential	(ODP) 0 0 0 0 Global	Warming	Potential	(GWP) (IPCC	2007) 13,396 5.5 3.3 0 4

EPA /SNAP Approval VLT	Freezers Requesting VLT	Freezers New	r etail stand

- alone refrigeration New	h ousehold refrigeration Safety	Group (ANSI/ASHRAE 2010) A1 A3 A3 A3

Maximum	charge quantity	[g] None Requesting 100 150 57

*	Minimum	ignition	energies	tend	to	be similar for	hydrocarbons (Kunz	1998)



### 3.2 VLT	Freezer	Study	Model

The	standard	freezer	chosen	for	thi s	study	is a - 86°C	780 liter	(27.5 cu.	ft.)	upright	(as	opposed to	 chest)	model	 referred	 to as	 the	 SU780U (Fig.	 3 )

. The	 SU780U	is	 an	 example	 of	 the	most
common	 size	 of	VLT	 freezer typically	 sold	 to	 bio

- repositories ,	 the	 pharmaceutical	industries
and	 universities

. In	 distinction	 to	 the	 universally	 applied	 cascade	 refrigeration	 systems,	 t his
unit utilizes	 a	 Stirling	 refrigeration	 system	 with	 a	 thermosiphon.	 For	 this	 study,	 the	 current thermosiphon	 charge	 of	 200g	 of	 R

- 508B	 has	 been	 replaced	 with	 100g	 of	 R

- 170	 (Ethane). Except	for	appropriate	labeling	and	marking,	the	R

- 170	unit	is	in	all	other	resp ects	identical	to
the	R

- 508B	unit.

4 According	to	manufacturer,	A.S.	Trust	and	Holdings.Confidential Global Cooling Inc. Page 10 June 2013 Fig.	3 Model	SU780U VLT	Freezer

As	 shown	 in	 Fig.	 1,	 the	 machine	 compartment	 of	 Stirling	 engine	 units	 is	 at	 the	 top	 of	 the cabinet.	Removing	the	top cover	of	the	freezer	provides access	to	all	the	essenti al mechanical components.	 Fig.	 4 shows	 the	 machine	 compartment with	 the	 top	 cover	 removed

. The thermosiphon	(2)	is	shown	with	its	insulation	removed.	 It	is	attached	to	the	cold	head	of	the Stirling (1) and	enters	the	cabinet through	a	collar to	surround	the	i nner	liner. There	are	four braze	 connections	 that	 are	 made	 in	 the	 mechanical	 compartment	 when	 attaching	 the thermosiphon	 to	 the	Stirling	engine. The	 thermosiphon	 fill	 tube	cannot	be	clearly	seen	but	it enters	 the	 thermosiphon	 condenser	 at	 the	 cold	 head	 of the	 Stirling	 engine. The	 electronic boards	 are	 shown	 at	 (3),	 (4)	 and	 (5).	 The	 inverter	 board	 is	 (4)	 and	 is	 the	 most	 relevant	 to safety	issues,	as	will	be	discussed	later.	Other	items	of	interest	is	the	door	switch	(14),	battery (12)	and	the	two	fans	at	(10 )	and	(11).Confidential Global Cooling Inc. Page 11 June 2013 Fig.	4 Major	Components	in	the	Machine	Compartment



### 3.3 Use	P rofile	of	VLT	Freezers
VLT	 freezers	are	generally	 clustered	 from	 perhaps	as	 few	as	 five or	 six	 units	 side	 by	 side	 to many	hundreds	within	a	large	building	in	 the	 form	 sometimes	 referred	 to	as	a	 freezer	 farm. This	 study	 will	 consider	 risks	 associated	 with	 end

- use.	 Transportatio n	 risk will	 not	 be
evaluated	since	it is	already	handled under	49	C FR	173.174	(refrigerating	machines).	UN	3358 Class	 2.1	 REFRIGERATING	 MACHINES	 containing	 flammable,	 non

- toxic,	 liquefied	 gas.	 IATA special	provision	A103 also	applies. Cold Head

Collar Braze Connections Thermosiphon condenser surrounds the cold headConfidential Global Cooling Inc. Page 12 June 2013 

### 3.4 Data	References
No	 safety	 data	 exists	 for	 the	 subject	 situation	 of	 a	 VLT	 freezer	 with	 Stirling	 refrigerating system.	 We	 therefore	 had	 to	 assemble	 close	 equivalent data	 that	 was	 sourced	 from	 the following:

a. Risk	Assessment	of	Flammable	Refrigerants	for	Use	in	Home	Appliance s	by	Arthur	D.	Little,
Inc. (Arthur	D.	Little	1991)
b. Use	of	R290	in	Ice	Cream	Cabinets	by	Unilever

.

c. Tests	done	under	Global	Cooling	Inc.’s	commission	by	UL	according	to	test	standard	UL471.
This	standard	has	been	revised	in	Novem ber	2012	to	include	laboratory	refrigerators	and
freezers.
d. ASHRAE	15

- 2010,	Safety	Standard for	Refrigeration	Systems (ANSI/ASHRAE	2010)

.
e. Combustion	studies	specifically	addressing R

- 170	( ethane )

.



### 4 D ET AILED 

### D ESCRIPTION	OF	THE 

### P RODUCT



### 4.1 The	Stirling	Engine
The	Stirling	engine	employs	Helium	gas	as	its	working	medium	in	a	closed	cycle.	There	is	no phase	 change	 of	 the	 working	 medium.	 The	 cycle	 compresses	 and	 expands	 the	 gas	 in segregated	areas	in	order	to	provide	a	cold	heat acceptor (also	referred	to	as	a	cold	head) and a	warm	heat	rejecter.	The	configuration	used	in	this	product	is	a	free

- piston	arrangement.	The
free

- piston	 arrangement	 uses	 no	 mechanical	 linkages;	 the	 moving	 parts	 are	 moved	 by	 a combination	 of	gas	 pressure	 f orces,	 springs	and	a	linear	motor.	No	 oil	is	 used,	lubrication	is provided	 by	 gas	 bearings	 and	 consequently	 very	 long	 life	 and	 high	 reliabilities	 are	 assured. Since	 there	are	no	mechanical	linkages,	 the	amplitude	of	 the	piston	can	be	controlled	by	 the appl ied	voltage.	This	allows	the	heat	lifting	capacity	of	the	unit	to	be	controlled.	Controlling	the capacity	 in	 this	 manner	 is	 in	 strong	 distinction	 to	 conventional	 compressors,	 which	 adjust their	 cooling	 effect	 by	 on/off	 modulation. Figure	 5 shows	 the	 basic arrangement	 o f	 a	 free

piston	Stirling	engine	with	 some	 of	 the	important	 parts	 noted. The	 particular	model	 used	in
the	 SU780U	 freezer	 is	 the M600,	 also	 manufactured	 by	 Global	 Cooling	 Inc.	 The	 M600 is pressurized	 to	 30bar	 (abs)	 with	 helium	 gas. Maximum	 input is	 1.2 kW and minimum/ maximum	 voltage	is 108/ 2 64 VAC (Global	 Cooling	 Inc.	 2013)

. At	 steady	 state	 conditions,	i.e., when	the	target	temperature	is	reached,	the	controller	backs	off	the	power to	around	300W	by reducing	the	input voltage.Confidential Global Cooling Inc. Page 13 June 2013 Fig.	5 Free

- Piston Stirling	Engine	Details (Schematic)



### 4.2 The	Thermosiphon
The	thermosiphon	is	a	3/8	inch	copper	tube	that	wraps	around	the	inner	liner	of	the	 freezer and	connects	the	thermosiphon	condenser	on	the	Stirling	engine.	It	is	hermetically	sealed	by	a pinch

- off	tube	a nd	contains	only refrig erant,	in	this	case	R

- 170.	There	are	no	internal	moving parts	 in	 contact	 with	 the	 refrigerant.	 The	 general	 arrangement	 of	 the	 thermosiphon	 can	 be seen	in	Fig.	1. The	thermosiphon	operates	at	the	saturation	pressure	of	the	refrigerant	for	that operating	tem perature.	For	example,	if	the	acceptor	of	the	Stirling	is	at

- 90°C,	then	refrigerant condensation	 takes	 place	 at	 the thermosiphon	 condenser	 at	 0.938bar.	 This	 condensate	 runs down	 the	 thermosiphon	 by	 gravity	 and	 evaporates	 in	 the	 tubing	 section,	 which	 is	 th e equivalent	of	the	evaporator	of	a	conventional	compressor	system.	Since	the	tube	is	essentially unrestricted,	the	evaporation	pressure	and	the	condensation	pressures	are	the	same	(different only	 due	 to	 the	 vapor	 pressure	 drop and	 gravity which	 is	 very	 sm all)	 and	 therefore	 the temperature	 of	 both	 the	 evaporation	 and	 condensation	 sections	 are	 almost	 identical.	 This condition,	 called	 isothermal	 heat	 transfer,	 is	 extremely	 efficient.	 Characteristics	 therefore	 of the	thermosiphon	are:

a. Isothermal	heat	transfer
b. Operates	at	any	temperature	below	the	critical	point,	in	this	case	32.2°C

Electrical Power Input Thermosiphon Condenser

Heat Rejecter (warm head) Thermosiphon Connector Displacer Piston

Linear Motor Passive Balancer Acceptor (cold head)Confidential Global Cooling Inc. Page 14 June 2013 c. No	internal	moving	parts.
d. Very	low refrigerant charge	for	a	given	heat	transfer rate

. In	this	case	100g	or	less.

e. No	oil	that	may	clog	capillary	tubes,	a	known	difficulty	with	convent ional	compressors	in the	VLT	application.
f. No	driers	or	other	components	that	may	complicate	servicing.



### 4.3 Heat	Rejection
Blowing	 air	 past	 radial	 fins	 at	 the	 heat	 rejecter	 rem oves	 the	 heat	 from	 the	 system.	 Two variable	 speed fan s	are used in	 series	 so	as	 to	 provide	 high	 rejection	 of	 heat	 during	intense cooling	 periods	 such	 as	initial	 cool	 down	 and	 door	 openings. The	 two

- fan	 arrangement also serves	 to	improve	 reliability	of	 the	system	since	 the	system	will	operate	with	one	 fan but at reduce d	capacity.	T he	Stirling	engine	is	much	more	efficient	t han	its	compressor	counterparts
and	therefore the	amount	of	heat	rejected	is	roughly	half	that	of	similarly sized	conventional systems .	Room	air	is	drawn	in	through	a	grill	above	the	door ,	passes through	a	tunnel	and	over the	rejecter	 fins	on	the	Stirling,	through	the	machine	compartment and	rejected	at the	upper right	side	of	the	freezer.	The	air picks	up	heat	from	the	electronic	controller	as	well.	The	flow of	air	is	one	pass	and	the	distance	fro m	the	inlet	to	the	outlet	is	about	700mm. The	maximum
volumetric	flow	is	214CFM

.


### 4.4 Electronic	Components
The	SU780U	is	able	to	take	universal	input	voltages.	The	line	voltage	is	converted	to	DC	voltage by	the	power	electronics and	this	is	provided	to	an	inve rter	that	provides	alternating	current to	the	Stirling	engine	at	a	fixed	frequency	but	a	variable	voltage	depending	on	cooling	demand. Electrical	 components	 must	 be	 evaluated	 for	 possible	 ignition	 sources.	 Compared	 to	 typical VLT	freezer	cascade	systems,	t he	Stirling	refrigeration	system	has	a	number	of	key	differences regarding	 the	 electrical	 system .	 The	 following	items	 are typically noted	 as	 potential ignition

sources (Arthur	D.	Little	1991) :

a. Thermostat	or	t emperature	control	s witch.	Typical	on	/	off	systems	have	a	make	/	break switch	 to	 turn	on	 the	compressor	when	 the	 temperature	is	 too	high	and	 turn	it	off	when the	 temperature	is	 too	low. The	 thermostat	is	located	in	 the	cold	space	and	switches	line voltage.	 The	 Stirling system	 uses	 a	 temperature	 transducer	 called	 an	 RTD , which	 is energized	by	a	continuously	connected low voltage	source of	5VDC

. The	RTD	is	completely encapsulated	by	a	metal	sleeve.
b. Defrost	control,	heater	and	thermostat.	These	items	are	not	used	in	VLT	fre ezers.

c. Energy	saver	switch.	This	item	is	not	used	in	the	SU780U.Confidential Global Cooling Inc. Page 15 June 2013 d. Interior light.	This	item	is	not used	in	VLT	freezers.

e. Automatic	icemaker.	This	item	is	not	used	in	VLT	freezers.
f. Cabinet	 or	 gasket	 heaters.	 Resistance	 heaters	 are	 used	 in	 many	 VLT	 freezer	 ca binets	 to warm	critical	areas	so	as	to	prevent	sweating	on	the	exterior	surfaces	of	the	cabinet	or	on the	 gasket. In	 the	 SU780U,	 these heaters	 are	 placed	 beh ind	 the	 thermal	 breaker	 on	 the
front	surface	of	the	cabinet.	The	thermal	breaker	on	the	door	is	no t	heated. For	R

- 170	units,
a	solid

- state	switch	driven	by	a	controllable	duty	cycle	modulates	the	gasket	heaters

. The	 following	 items	 are	 specific	 to	 the	 Stirling	 system	 and	 are	 listed	 as	 potential	 ignition

sources:

a. Thermal	limit	switch	(called	out	as	a	 t hermal	 fuse in	 the	schematic	diagram,	Fig.	6 ).	This item	opens	 the	circuit	 to	 the	Stirling	engine	when	 the	outside	surface	 temperature	of	 the Stirling	 engine	 exceeds	 110°C.	 This	 is	 only	 likely	 to	 happen	 in	 a	 locked	 reciprocator condition	(equivalent	to	a	l ocked	rotor	condition on	conventional	systems ).
b. Door	alarm	switch.	This	item	signals	an	alarm	to	sound	if	the	door	has	been	open	beyond	a user	specified	time. The	switched	voltage	is	3.3VDC.

c. Dry	 contact	 relay.	This	is	energized when	an	alarm	 condition	exis ts	according	 to	 several user	settable	conditions.	The	maximum	allowed	switched	voltage	is	24VDC.
d. Power	switch.	This	is	where	the	SU780U	is	switched	on.	It	is	located	at	the	top	rear	of	the freezer	next	to	the	line	cord.	The	line	voltage	is	rated	from	108	t o	264VAC,	50	or	60Hz.

e. Battery	 switch.	 This	 is	 to	 energize	 a 6V backup	 battery	 to	 maintain	 temperature monitoring	and	storage	of	critical	information	during	a	power	failure. It	is	located	near	the power	switch.
f. Line	fuse.	Two	line	fuses	are	used	to	the	power	board	and	two	to	the	Stirling	engine.	These are	sealed	devices	 that	permanently	open	circuit	when	current	conditions	 for	 those	lines are	exceeded.	They	are	located	in	the	machine compartment

. g. Inverter	board. The	Stirling	engine	takes	an	AC	input and adjusting	this	AC	voltage	controls the	capacity	of	the	Stirling .	The	inverter	board	takes	DC	power	from	the	power	board	and converts	it	 to	a	 controlled	AC	 voltage	 by	 use	 of	an	H

- bridge	 circuit.	 The	H

- bridge	 circuit components	are	capable	of	energetic	failure.	We	calculate	that	the	energy	liberated	in	such a	failure	to	be	75J.	Well	above	the	MIE	of	R

- 170.

The	electrical	schematic	f or	the	SU780U	is	shown	in	Fig.	6

.Confidential Global Cooling Inc. Page 16 June 2013 Fig.	6 Electrical	Schematic	Diagram	for	the	SU780U Freezer PCB

Ͳ GUI

Ͳ 4.1: User Interface

PCB

Ͳ M6

Ͳ INV: Inverter Board

PCB

Ͳ M6

Ͳ PWR: Power Board

Line Filter

Ͳ SCHAFFNER FN2070

Ͳ 12

Ͳ 06

Ͳ UL E3087691

AC Power Switch DPDT

Ͳ Cherry WRG32F5FBBNN

Ͳ UL E23301

AC Power Input Receptacle

Ͳ Qualtek 703W

Ͳ 00/04

Ͳ UL AXUT2.E139592 Non

Ͳ Line Isolated H

Ͳ Bridge

Non

Ͳ Line Isolated Power Supply 5Vdc @ 2A

Ͳ CUI VSK

Ͳ S5

Ͳ 15UA

Ͳ UL E222736 12Vdc @ 2.1A

Ͳ CUI VSK

Ͳ S25

Ͳ 12U

Ͳ UL E222736 24Vdc @ 1.66A

Ͳ TDK

Ͳ Lambda KMS40

Ͳ 24

Ͳ UL E135494 Non

Ͳ Line Isolated Power Supply 380Vdc @ 5A

Ͳ COSEL DPF1000

Ͳ UL E132067 15Vdc @ 333mA

Ͳ CUI VSK

Ͳ S5

Ͳ 15UA

Ͳ UL E222736

Line Filter 120/240VAC @ 16A

Ͳ Schurter FMBA

Ͳ 0172

Ͳ 1670

Ͳ UL EN133200

Line Fuse

Ͳ Littelfuse 0314012.HXP

Ͳ UL E10480 Line Fuse

Ͳ Littelfuse 0314012.HXP

Ͳ UL E10480 TVS

Ͳ Littelfuse V275LA20AP

Ͳ UL E320116, E56529, E135010

Earth Ground M600 Stirling Cooler PCB

Ͳ M6

Ͳ ACCEL:

Ͳ Global Cooling Inc.Accelerometer

RTD (Cold Head Temperature)

Ͳ JMS Southeast 17436C

Thermistor (Warm Site Temperature)

Ͳ Cantherm CWF3AA103G3380

M600 Coil

Ͳ Global Cooling Inc UL

....

M600Fan

Ͳ Nidec X17L24BHM5

Ͳ 06 Optical Isolator Avago HCPL

Ͳ 073A

Ͳ UL FP Q U2.E55361 RS232 Communication

Ͳ Texas Instruments MAX232DR

Ͳ UL... RS232 Communication

Ͳ Texas Instruments MAX232DR

Ͳ UL...

Current Sense Transformer

Ͳ CR Magnetics CR8348

Ͳ 2000

Ͳ UL XODW2.E235509 Voltage Sense Transformer

Ͳ Tamura Power Transformer 3FD

Ͳ 212

Ͳ UL XOKV2.E95844

Microprocessor Microchip Technology PIC18F6722

Ͳ I/PT

(10.0 MHz Operating Frequency) 5V 12V

Power Supply Status Signals

Electronics Fan

Ͳ Nidec X17L24BHM5

Ͳ 06 Control Feedback Signals

Gasket Heater

Ͳ Springfield Wire 34152

Ͳ 55 W (2333 Ohms) Gasket Heater Relay

Ͳ TE Connectivity RZ01

Ͳ 1A4

Ͳ D005

Ͳ UL E214025

380 Common

+ 380Vdc LCD Display Driver

Ͳ Solomon Systems SSD1963QL9 Ethernet Driver (Not Used)

Ͳ Microchip Technology ENC624J600

Ͳ I/PT (4.0 MHz Operating Fre q uenc y ) Real Time Clock With Lithium Battery

Dry Contacts Relay

Ͳ TE Connectivity RZ01

Ͳ 1A4

Ͳ D005

Ͳ UL E214025 Battery Charge Controller

Ͳ Texas Instruments UC2906DW

Ͳ UL Microprocessor

Ͳ Microchip Technology PIC32MX360F512L (8.0 MHz Operating Frequency) Auxiliary Relay (Not Used)

Ͳ TE Connectivity RZ01

Ͳ 1A4

Ͳ D005

Ͳ UL E214025 LCD

Ͳ Sharp LQ070Y3DG3B

Buzzer

Ͳ PUI Audio X

Ͳ 4033

Ͳ TF

Ͳ LW80

Ͳ R RTD (Box Air Temperature)

Ͳ JMS Southeast 17436D

Door Switch

Ͳ Omron Electronics D3D

Ͳ 221

Ͳ UL WOYR2.E41515

Thermal Fuse

Ͳ Sunshine KSD301

Ͳ P

Ͳ UL XAPX2.E213536 RTD

Ͳ JMS Southeast 17436D Battery

Ͳ Panasonic

– BSG LC

Ͳ R067R29

Ͳ UL BAZR2.MH13723

Line Fuse

Ͳ Littelfuse 0216008.HXP

Ͳ UL E10480

Line Fuse

Ͳ Littelfuse 0216008.HXP

Ͳ UL E10480

Line Fuse

Ͳ Littelfuse 0326008.MXP

Ͳ UL E10480Confidential Global Cooling Inc. Page 17 June 2013 

### 5 G AS 

### L EAKAGE 

### E VENTS



### 5.1 Manufacturing	Site
There	 are	 two	 items	 that	 require	 leak	 testing.	 The	 first	 is	 the	 Stirling	 engine,	 which	 having
bein g	charged	with	helium	is placed	in	a	vacuum	chamber	with	a	helium	leak	detector.	There	is a	 leakage	 threshold	 that	 conforms	 to	 at	 least	 a 10

- year	 useful	 life.	 If	 the	 unit	 meets	 that criterion,	 then	 it	 is	 passed	 for	 integration	 with	 the	 cabinet.	 The	 second	 item	 is	 the thermosiphon, which	 is	 charged	 with	 R

- 170.	 Leakage	 from	 this	 item	 is	 considered	 a	 safety issue	due	to	the	flammability	of	R

- 170. The	thermosiphon	evaporator	section	is	sourced	from	a supplier.	As	purchased,	it	has three brazed	joints	 that	are	certified	leak

- free	by	 the supplier. The	 M600	 Stirling	 engine	 is	 attached	 to	 the	 thermosiphon	 by	 brazing	 two	 elbow	 tubes between	the	thermosiphon	evaporator	and	the	thermosiphon	condenser.	The	total	number	of shop

- brazed	 joints	 is	 four.	 The	 fill	 tube	 is	 attached	 to	 the	 thermosiphon condenser	 by	 the
vendor of	the	Stirling	head	assembly and	is	certified	to	be	leak

- free.	A	silver

- soldered	joint	is made	 on	 the	 fill	 tube	 to	 extend	 it	 so	 that	 it	 can	 be	 conveniently	 pinched	 off	 after	 the thermosiphon	has	been	charged.	The	charging	process consists	of	attaching	a	vacuum	pump	to
a	manifold	that	attaches	to	the	fill

- tube.	A	vacuum	is	pulled	on	the	thermosiphon	to	less	than
60	micro

- Torr and	held	for	15	minutes

. Any	unacceptable	leak	will	not	allow	a	vacuum	of	this
level	to	be	maintained.	This step	confirms	the	integrity	of	the	thermosiphon.	An	R

- 170	cylinder is	 also	 attached	 to	 the	 vacuum	 manifold	 by	 way	 of	 a	 valve	 and	 capillary	 line.	 Once	 the evacuation	process	has	been	completed,	a	valve	to	the	vacuum	process	is	closed	and	R

- 170	gas
is	allowe d	 to	enter	 the	 thermosiphon	by	opening	a	valve	in	 the	capillary	line.	The	amount	of gas	charge	is	determined	on	a weight basis	by	an	electronic	scale. Once	the	correct	charge	has been	placed,	the	valve	is	closed	and	the	fill

- tube	is	pinched

- off	with	a	spec ial	tool	to	form	a	gas tight	seal. Removal	of	the	remaining	piece	of	the fill

- tube	from	the	manifold	results	in	a	leakage of	about	0.02g.



### 5.2 Servicing	Site
If	 for	any	 reason	 servicing	is	 required	where	 the	Stirling	engine	must	be	 r emoved,	it	will	be

necessar y	 to	 remove	 the	 refrigerant. The	 device	 recommended	 for	 this	 purpose	 is	 the Caresaver	Universal	 Refrigerant	 Recovery	Unit.	 The	 unit	 has	 an	 onboard	 storage	 capacity	 of 250g,	 which	is	 sufficient	 for	 two	 SU780U units charged	 with	 R

- 170 .	 In	 order	 to	 remove	 the refrigerant,	 the	 thermosiphon	 fill	 tube	 will	 be	 penetrated	 with	 a	 refrigerant	 servicing	 tool.
Connectio ns	to	this	tool	will	be	by	Schra der	valve ,	which	opens	only	when	a	properly	equipped refrigerant	hose	is	fully	seated	onto	the	valve.	No	significant	ref rigerant	leakage	is	anticipatedConfidential Global Cooling Inc. Page 18 June 2013 during	 the	 removal	 of	 the	 refrigerant.	 However,	 when	 the	 refrigerant	 is	 returned	 to	 an appropriate	 cylinder,	 leakage	 is	 anticipated	 when	 the	 refrigerant	 hose	 is	 detached	 from	 the cylinder.	The	amount	of	refrigerant	leaked	is what	resides	within	the	Schrader	valve	when	it	is disconnected.	 We	 estimate	 that	 to	 be	 0.02g.	 We	 anticipate	 a	 similar	 leak	 when	 the thermosiphon	is	refilled	after	repair	and	the	refrigerant	hose	is	disconnected.	We	anticipate	no leakage	after	repair	since the	tube	is	sealed	by	a	pinch	off	tool	that	has	exceptional	reliability for	this	purpose.



### 5.3 Non

- Conforming	Leaks

Leaks	 that are	 not	 anticipated	 during	 the	 normal	 course	 of	 business	 are	 referred	 to	 as	 non

conforming	leaks.	The	probabilities	of	these	leaks	ar e	designed	to	be	low	and	their	occurrences are	assumed	to	be	at	probability	levels	on	par	with	household	refrigerators.	At	the	factory,	we believe	that	leakage	from	a	braze	joint	sufficiently rapid	to	cause	an	explosive	accumulation	of gas	is essentially nil .	W e	 would	 not	 be	 able	 to	 effectively evacuate the	 thermosiphon	 to	 the required	vacuum	level	if	it	had	such	a	leak.	However,	during	transportation,	the	VLT	freezer	is subjected	 to	 transport	loads	 that	 are	 only	 statistically	 understood.	 Some	 of	 these	lo ads	may subject	the	braze	joints	to	excessive	loads	or	fatigue	situations	that	could	result	in	damage	and therefore	 leakage. The	 process	 of	 sealing	 the	 fill

- tube	 by	 the	 pinch

- off	 method	 has	 been identified	as	a	potential	source	of	non

- conforming	leak.	 If	 t he	inside	of	 the	copper	 fill

- tube	is not	 perfectly	 clean	 or	 has	 residual	 oil,	 it	 is	 possible	 that	 the	 pinch

- off	 will	 not	 be	 100% effective.	We	test	every	pinch

- off	seal	for	leakage	by	use	of	a	soap	solution	(residue	is	cleaned with	alcohol).	If	a	leak	is	d etected,	it	will	be	a	slow	leak	and	it	will	be	into	the	surrounding	air since	 the	 freezer	 machinery	 compartment	 will	 not	 be	 closed.	 The	 freezer	 will	 also	 not	 be operating,	so	its	ignition	sources	will	not	be	energized. From	our	own	experience,	such	a	leak occurs	about	once	in	100	freezers.	For	a	less	experienced	assembler,	this	leak	may	occur	once in	 50	 freezers.	 In	 any	 case,	 leakage	 to	 atmospheric	 pressure	 is	 in	 excess	 of	 one	 hour	 and	 a second	pinch

- off	is	executed	within	three	minutes	of	the	first	since	t hat	is	how	long	it	takes	to determine	the	effectiveness	of	the	seal.	Rarely	do	we	see	a	need	for	more	than	two	attempts	to pinch	off	the	fill

- tube.
Leaks	due	to	transportation	loads	are	rare	but	do	occur. We	will	estimate	this	event	based	on
the	Arthur	D. Little	report	even	though	the	thermosiphon	has	far	fewer	joints	subject	to	such loads	 than	 household	 refrigerators	 have. Of	 course,	 the	 freezer	 is	 not	 operational	 during transport	and	therefore	none	of	its	ignition	sources	will	be	relevant during	transport

.Confidential Global Cooling Inc. Page 19 June 2013 Non

- conforming	leaks	during	servicing	are	also	anticipated	at	the	pinch

- off	tube and	with	the same	 likelihood	 as	 during	 manufacture.	 Braze	 joints	 made	 during	 servicing	 will	 be	 verified during	 the	 evacuation	 process	 and	will	 not	 provide	 the	 required	 vacuu m	level	if	 they	 suffer from	any	significant	leaks.



### 6 R ISK 

### A SSESSMENT



### 6.1 Introduction
Statistical	 leak	 data	 is	 assumed	 to	 be	 identical	 to	 that	 identified	 by	 household	 refrigerator
manufactures	 for	 similar	 conditions	 and	 circumstances. ADL (Arthur	 D.	 Little	 1991) did consequence	modeling	to	define	refrigerant	charge	release	and	duration	that	would	constitute a	catastrophic	release	of	flammable	refrigerant.	They	found	that	combustion	of 50g	of R

- 152a would	achieve	an	overpressure	of	0.2bar (3psi) in	a	typi cal	kitchen	of	a	floor	size	of	180	sq.	ft. and	ceilings	of	8	ft. The	kitchen	is	also	assumed	to	have	a	single	door	(3ft.	by	7ft.)	and	a	single window	(2ft.	by	3ft.). R

- 152a	is	in	the	ASHRAE	sa fety	group	A2	and	its	flammability	limits	are 4.8	to	17.4%	by	volume	with	a	heat	of	combustion	at	17.4MJ/kg. Table	2,	taken	from	the ADL report,	lists	the	biological	and	damage	consequences	for	different	overpressures. Fig.	7	shows
their	simulation	results of	overpressure	versus	R

- 152a	mass	for	a	confined	typical	kitchen.

Table	2	Biological	and	Structural	Damage	Consequences	from	Explosion (Arthur	D.	Little	1991)
Overpressure [psi]* Biological Damage Structural Damage

70 99% Fatality Total structural damage 50 50% Fatality Total structural damage 35 1% Fatality Total structural damage 15 Lung damage Severe structural damage

7

- 8 Shearing and flexure failure of brick wall panels, 8 to 12 inches thick (not reinforced)
5 Eardrum rupture Shattering of concrete wall panels, 8 to 12 inches thick (not reinforced)

2

- 4 Non

- reinforced cinderblock walls shattered; 50% destruction of brick buildings; steel frame building distorted; light industrial building ruptured.
1

- 2 Failur e of wood siding panels. Shattering of asbestos siding and corrugated steel and aluminum panel failure. 0.1

- 1 Shattering of glass windows. *Note that the total overpressure may be achieved by reflection of an incident wave of about half of the stated values

.Confidential Global Cooling Inc. Page 20 June 2013 Fig.	7 Overpressure [bar] from	Combustion in	a	Typical	Kitchen versus	R

- 152a Mass [kg] (Arthur	D.	Little	1991)

In	order	to	apply	this	data	to	R

- 170,	we	note	from	Table	1	that	the	heat of	combustion for	this refrigerant	is	51.9	MJ/kg	versus 17.4	MJ/kg	for	R

- 152a.	We	will	assume	that	the	pressure	rise is	 directly	 proportional	 to	 the	 heat	 of	 combustion	 (this	 assumption	 does	 not	 include dissociation	energy	so	it	is	approximate).	That	suggests	that	R

- 170 will	have	roughly	3	times

more pressure	generation	than	R

- 152a for	the	same	mass	of	charge

. Bio

- storage	facilities	and laboratories	 have	 at	 least	 10ft	 ceilings (Carnegie	 Mellon	 University	 2007) and	 are	 typically open	 spaced	 co nstruction.	 We	 will	 consider	 a	 worst

- case	 scenario	 where	 VLT	 freezers	 are placed	side

- by

- side	in	a	laboratory	hallway 10ft	wide	by	30ft	long	with	no	windows.	Assuming that	the	pressure	rise	is	essentially	adiabatic,	we	can	scale	the	effect	of	the	larger	ro om	by	the adiabatic	law.	This	gives	a	pressure	ri se	of	about	0.2bar	(3psi)	 for deflagration of	R

- 170	in	a laboratory	environment,	almost	identical	 to	 the	R

- 152a	situation	in	a	kitchen. Of	course,	 this assumes	50g	mass	as	was	used	in	the	kitchen	study.

The rate	of	pressure	increase	is	an	important	factor	i n	an	explosion and	is	determined	by	the deflagration	index K G (NFPA	2013) .	Comparative deflagration	index	data for	n

- Butane	and R

170	(ethane) are	show n in	Fig.	8 (Holtappels	2002)

. For	comparison,	the	maximum	value	of K G of	propane	is	100	bar

- m/s (NFPA	2013)

. Data	for	ethane	from	a	second	source	is	shown	in	Fig.Confidential Global Cooling Inc. Page 21 June 2013 9.	In	this	case,	the	abscissa	is	the	equivalen ce	ratio Ø .	The	maximum K G is	similar	in	both	cases
at	about	1 3 0	bar

- m/s and	is	therefore	taken	as	confirmation	of	this	number.

Fig.	8	Deflagration	Index K G for	Ethane	and	n

- Butane

Fig.	9	Deflagration	Index K G for	Ethane	versus	Equivalence	Ratio (Kunz	1998)

.

Fig.	10	Peak Combustion Pressures	for	Ethane

- Air	Mixtures (Kunz	1998)
The	 peak	 pressure	 generated	 by	 constant

- volume	 combustion	 of R

- 170 is	 shown	 in	 Fig.	 10.
These	 numbers	 are about	 5%	 lower	 than	 what	 would	 be	 expected	 at	 AICC	 conditions.	 Data from	technical	University	Delft (Holtappels	2002) show	similar	results	and	confirm	the	general magnitude	 of	 the	maximum	generated	pressure though,	NFPA	 show	a	maximum	pressure	 of Initial Conditions: 1bar and 295K (22°C) Initial Conditions: 1bar

Initial Conditions: 1bar and 295K (22°C)Confidential Global Cooling Inc. Page 22 June 2013 only	7.8bar (NFPA	2013) for	R

- 170

. The	fundamental	burning	v elocity	of	ethane	is	(47cm/s), which	is	similar	 to	propane	(46cm/s)	and	n

- butane	(45cm/s). Determining	 the	overpressure in	 a	 practical	 situation,	 say	 the	 machine	 compartment,	 from	 a	 deflagration	 event	 requires complicated	three

- dimensional	modeling.	Howeve r,	we	believe	that	the conditions	modeled	by Unilever	 for	 ice	 cream	 cabinets	 closely	 resemble our	 situation (Unilever	 2008) .	 Unilever modeled	 a	 combustion	 event	 under	 stoichiometric	 and	 perfect	mixing	 conditions	 within the compressor	compartment	of	an	ice	cream	cabinet assuming	R

- 290	(propane)	as	the	refrigerant. This	is	not	too	different	from	our	machine	compartment,	which	is	equipped	with	vents	for	inlet and	 exhaust	 cooling	 air and	 is	 located	 at	 the	 top	 of	 the	 VLT	 freezer

. The	 Unilever	 model calculated	 an	 overpressure	 of	 0.1bar	 (1.5psi). A	 pressure	 of	 this	 magnitude	 would	 lift	 the machine	 compartment	 cover	 but	 would	 dissipate	 rapidly.	 In	 any	 event,	 a	 stoichiometric
mixture	in the	machine	compartment volume	 (0.14m 3 )	would	re present about	38g	of	R

- 170.
From	the K G value	for	R

- 170,	the	maximum	rate	of	pressure	rise	in	this	compartment	would	be
6 7

. 5 bar/s.
A	second	source	of	damage	or	injury	occurs	when	 the	 thermal	 radiation	 from	c ombustion	is sufficiently	large	and	 for	a	su fficiently	extended	time.	Fig.	11 ,	also	taken	 from	the ADL study,
shows	 the	 time required	 for	 pain	 sensation	 due	 to	 exposure	 to	 thermal	 radiation. ADL concluded	 that	 thermal	 radiation	 levels	 of	 about	 12.5	 kW/m 2 are	 sufficient	 to	 ignite combustibles	and	cause	pain,	but	are	not	sufficient	to	cause	serious	injury	after	exposures	of
one	second	or	less.

F ig.	 11 Time	 [s]	 Required	 to Reach	 Pain	 Threshold	 Due	 to Exposure	 to	 Thermal	 Radiation [kW/m2] (Arthur	D.	Little	1991)Confidential Global Cooling Inc. Page 23 June 2013 We	are	assuming	that	adiabatic	flame	temperature	is	a	measure	of	the	radia ted	energy	of	the
flame.	Table	3 lists the	adiabatic flame temperature	for	some	common	fuels	including	R

- 152a
all initially at	 1bar,	 20°C	 and s toichiometric	 for	 the	 fuel

- air	 mixture. From	 this	 table	 and knowing	that	thermal	radiation	is	a	strong	function	of temperature,	it	is	clear	that	e thane	has the	lowest	potential	for	thermally	radiated	burns.

Table	3 Adiabatic	Flame	Temperatures	for	Various Fuels (Wikipedia	2013)

Fuel Oxidizer Adiabatic Flame Temperature [°C] Butane (C4H10) Air 1970 R

- 170 Ethane (C2H6) Air 1955 Propane (C3H8) Air 2392 R

- 152a Air About 2600 (Bennett 2011)



### 6.2 Probability of Leaks

The ADL report	provides	leak	data	from	three	manufactu rers	of	household	refrigerators	over the	first	five	years	of	service.	By	assuming	that	the	manufacturer	tests	all	refrigerators	before shipment,	 they	 determined	 that	 units	 that	 arrived	 at	 their	 customers	 with	 insufficient refrigerant	must	have	lost	their	c harge	during	shipment.	This	was	deemed	the	best	measure	of catastrophic	leak	potential. We believe	that	this	is	the	best	indication	of	transport	damage to braze	 joints	 and	 the	integrity	 of	 the	 thermosiphon

. Arthur	 D.	 Little	 also	 argues	 that	 50%	 of

non - func tioning	refrigerators	occur	prio r	to	shipping.	This does	not	fit	our	assessment	since	all VLT	Stirling	 freezers	 are	 final	 tested	in	 three	 categories,	 namely	 a.	 Initial	 pull

- down	 time,	 b. steady

- state	 energy	 consumption	 and	 c.	 temperature	 recovery	 after	 doo r	 openings. This process	takes	about	12	hours	to	complete.	During	these	tests	the	thermosiphon	is	subjected	to high	 and	low	 pressures	 and	 temperatures	 from	 ambient	 to	 about

- 100°C.	 If	 any	 gas	leakage

were present,	it	would	be	at	an	extremely	low	rate	(less than	5%	loss	of	charge	in	12	hours)	to allow	 the	 VLT	 freezer	 to	 pass	 final	inspection. Therefore	 for	 purposes	 of	 estimating	leakage due	 to	 transportation	 damage,	 we	 will	 assume	 that	 the	 number	 for	 household	 refrigerators that	 are	 dead	 on	 arrival	 represent s	 a	 best	 estimate	 for	 this	 failure	 mode.	 This	 number, according	to	Arthur	D.	Little’s	investigation,	is	0.1%.

Arthur	 D.	 Little	 estimate	 that	 there	 are	 between	 11

– 14	 tubing	 connections	 in	 household refrigerators with	 4	 joints	 inside	 the	 cabinet cold	 spac e

. Two	 of	 these	 joints	 are	 copper	 to aluminum	 and	 were	 identified	 as	 the	 most	 likely	 to	 leak.	 All	 other	 joints	 are	 brazed

. In household	refrigerators,	50%	of	all	catastrophic	leaks	occur	within	the	cabinet	cold	space. The
VLT	 freezer thermosiphon	 has 7 bra ze	 joints	 and	 all	 are	 copper	 to	 copper

. Three	 of	 the thermosiphon	joints	 are	within	 the	 foamed	 section	 of	 the	 cabinet.	All	 other	joints	 are	in	 the machine	 compartment. Where	 the	 thermosiphon	 enters	 the	 Stirling,	 the	 joints	 there	 areConfidential Global Cooling Inc. Page 24 June 2013 stainless	 steel	 to	 copp er	 and	 th ose	 are	 vacuum	 brazed together	 with	 the	 Stirling	 cold	 head assembly .	The	1 /8

- inch copper fill

- tube extension and	 the	pinch

- off	joint are silver	soldered. No	 joints	 are	 inside	 the	 VLT	 fr eezer	 cabinet	 space

. These	 joints	 are	 shown	 in	 Fig.	 12

. A catastrophic	 leak	 into	 the cabinet	 could only	 occur	 if	 the	 16

- gauge (about	 1.6mm)	 stainless
steel (or	powder	coated	steel) inner	liner	were	punctured	sufficiently	and	at	the	right	place	to penetrate	the 3/8	inch copper thermosiphon	tube. VLT	freezers	are manually	defrosted	but	ice does	 not	 adhere	 to	 the	interior	 freezer	 walls,	 rather	it	 accumulates	 on	 the	 thermal	 breaker. Due	to	the	very	low	temperature	of	VLT	freezers,	wate r	vapor	tends	to	freeze	out	in	the	form
of powder	snow.	Removal	of	ice	from	the	br eaker	is	done	with	a	plastic	scraper	while	the	snow
in	 the	interior	is	 brushed	 out. Damage	 to	 the	plastic	 thermal	 breaker	would	not damage	 the thermosiphon	 since	 the	 thermosiphon is	 placed	 well	 back	 from	 the	 breaker	 surface	 and	 is encased	in	polyurethane	f oam.	We	are	unable	to	identify	any	plausible	event	that	may	achieve simultaneous	 penetration	 of	 the	 liner	 and	 thermosiphon	 tube	 that	 could	 result	 in	 a catastrophic	failure. In	addition,	there	are	no	ignition	sources	within	the	cabinet	cold	space	of
VLT	 fre ezers. We	will	 therefore assume	 that	all	 catastrophic	leaks	 occur within	 the	machine compartment,	which	we	feel make s the	numbers	more	realistic	for	our	situation.

We	 have	 reconstructed ADL’s household	 refrigerator	 data to	 include	 our	 belief	 that	 all	 fast leaks	occur	during	transportation	(defined	as	factory	dock	to	installation	at	customer)	and	that they	are	half	as	likely	to	occur	(no	copper	to	aluminum	joints)	and	that	all	slow	leaks	occur	in
use	at	the	end

- user’s	site. This	is	summarized	in	Table	4

.
Table	4 Modified	Leak	Rate	Data	Adjusted	from	Arthur	D.	Little	1991	Report % of refrigerators Manufacturer 0

- 7 days (DOA) Year 1 Total Years 2

- 5 Total Years 0

- 5 A 0.09 0.22 0.055 0.44 B

- 0.5 0.125 1.00 C 0.1

- - - Worst Case 0.1 x 0.5 = 0.05 0. 0 5 0.125 1.00 Shipping leak 0. 05 0. 05

- 0. 05 Slow leak 0 0.4 5 0.125 0.9 5 Fast leak 0.05 0. 05 0 0. 05 Average Case* 0.09 x 0.5 = 0.045 0.22 0.055 0.44 Shipping leak 0.045 0.045

- 0.045 Slow leak 0 0.175 0.055 0.395 Fast leak 0.045 0.0 45 0 0.045 *Average case is assumed by ADL to be the lower set of leak rates Catastrophic	 leakage	 during	 transportation	 could	 happen	 by	 the	 following	 mechanism.	 The tubes	are	insulated	in	 the	machine	compartment	by	 flexible	material	and	are	attached	 to	 the Stirling	 engine, which	 is	 soft	 mounted	 to	 the	 cabinet.	 Transportation	 loads	 could	 therefore subject	 the	 VLT	 freezer	 to	 vibrations	 that	 allow	 small	 relative	motions	 of	 the	 thermosiphonConfidential Global Cooling Inc. Page 25 June 2013 tubes	and	cause	 fatigue	damage.	Since	 the	 freezer	is	not	powered	during	 transportation	an d both	 the	 shipping	 container	 and	machinery	 compartment	 are	 not	 gas	 tight,	 we	 feel	 that	 the likelihood	 of	 accumulated	 gas	 is	 small.	 However,	 it	 seems	 possible	 under	 certain circumstances	that	some	gas	could	remain	in	the	machinery	compartment	up	the	point when the	VLT	freezer	is	first	switched	on.	A	simultaneous	failure	of	the	two	exhaust	fans	(L10	life	is 70,000	 hrs.	 for	 each	 fan)	 would	 exacerbate	 this	 situation.	 We	 will	 attempt	 to	 quantify	 this scenario	by	assuming	 that	 the	ignition	source	would	be	a	high

- energy	 failure	of	 the	H

- bridge
on	the	inverter	board	of	the	electronics	section.	We	have	seen	this	 failure	in	non

- conforming parts.	 Since	 this	is	 a	 failure	 that	 occurs	 on	initial	 power	 and	 each	 board	is	 pre

- tested,	 these failures	are	always	caught	before the	product	leaves	the	factory.	However,	we	will	assume	a	1 in	 1,000	 chance	 of	 an	 electronic	 failure	 at	 the	 delivery	 site	 (based	 on	 2	 sigma	 normal distribution	 on	 current	 units	 in	 the	 field).	 Since	 there	 are	 at	 least	 10	 discrete	 sections	 that
must	 all	 func tion	 properly	 for	 the	 electronics	 to	 start	 up,	 we	 will	 assume	 that	 an	 H

- bridge
failure	is	a	1	in	10	chance.
Slow	leakage	 from	imperfect	braze	joints	are	possible	but	 they	would	have	 to	be sufficiently small	as	to	allow	the	evacuation	process	of	the	thermosiphon	to	proceed	normally.	To	test	this scenario,	we	installed	capillary	tubes	to	all	braze	joints	within	the	VLT	cabinet	and	requested UL	to	test	for	potential	refrigerant	leakage	into	th e	cabinet.	We	do	not	have	their	official	report as	of	this	writing,	but	in	speaking	to	the	UL	manager	of	the	project,	interior	space	leakage	has not	been	a	problem.

Fig.	12 Inner	Liner	of VLT Stirling	Freezer Showing Thermosiphon	Joints Joint 2 and 3 on either side here

Joint 1 Inner Liner Joint to Stirling Engine (completed after cabinet is foamed)Confidential Global Cooling Inc. Page 26 June 2013 

### 6.3 Failure	Rate	Estimates
Failures	that	could	ignite	a	catastrophic	leak	within	the	machine	compartment	are	as	follows:

a. A	bad	power	switch	where	an	arc	with	sufficient	energy	is	present.
b. An	energetic	failure	of the	electronics	at	initial	power	on.	We	believe	that	this	is	only	likely
on	the	H

- bridge	section	of	the	inverter (Fig.	6) .	All	electronics	are	pretested	and	run	for	at least	 12	 hours	 before	 the	VLT	 freezer	is	 shipped.	We	 have	 not	 seen	 such	a	 failure	in	 the field	but	nevertheless,	we	will	assume	a	field	failu re	of	the	electronics	at	1	in	1 ,000	and	a
likelihood	 of	 the	 failure	in	 the	H

- bridge	as	 1	in 10	and	 further,	 that	 the	 failure	is always energetic	enough	to	i gnite	the	gas	mixture

.

c. A requirement	is	that	the	gas	mixture	be	resident	in	the	machine	compartment.	For	this	to happen,	 both	 fans	 must	 have	 failed	 simultaneously.	 	 The	 fans	 are	 also	 tested	 before shipment	but	nevertheless;	 their	L10	lives	are	70,000	hours	(about	8	years).	That	m eans that	 10%	 of	 the	 fans	 fail	 in	 that	 time	 or	 0.0125/yr.	 For	 two	 fans	 simultaneously	 this
becomes	1.56	x	10

- 4 /yr.

We are	excluding	the	following items	as	potential	ignition	sources	at	start	up :

a. A	 locked	 rotor	 or	 armature	 condition.	 This	 is	 characterized	 b y	 the	 moving	 components becoming	locked	within	the	Stirling	engine.	The	applied	power	therefore	heats	the	engine and	perhaps	 to	a	high	enough	 temperature	 to	ignite	 the surrounding gas	mixture.	 In	 this situation,	 the	 thermal	 fuse	 would	 have	 to	 fail	 to	 allow the	 Stirling	 engine	 t o	 heat	 up.	 In addition,	with	a failed	 thermal	 fuse,	 the	Stirling	would	 take	a	number	of	hours	 to	reach	a high	 enough	 temperature	 so	 we	 feel	 that	 it	 is	 unlikely	 for	 that	 the	 gas	 not to have dissipated	by	then.
b. The	gasket	heater	relay. We	have	repla ced	this	item	with	a	solid

- state switch	based	on	UL’s
recommendation. There	will	be	no	gasket	heater	relay	in	SU780Us	using	R

- 170.

c. Door	alarm	switch.	This	circuit	is	only	energized	after	the	init ial	pull	down	to	temperature.
d. Dry	contact	relay .	This	is	for	an	external	alarm	circuit	and	is	energized	after	the	initial	pull down	to	temperature.

Table 5 summarizes	 the	 failure	 rate	 estimates for	 potential	 ignition	 sources	 within	 the machine	compartment

.Confidential Global Cooling Inc. Page 27 June 2013 Table	5 Failure	Rate	Estimates for	an	Internal	Event Event Description Frequency of Probability Source / Discussion

1.1 Sudden release 0.0005/5 = 1x10 - 4 /yr From Table 3

1.2 Leak occurs at delivery 30/(7 x 24 x 60) = 3x10 - 3 Assume one week for delivery with probability of fault occurring in last 30 minutes 1.3 Two exhaust fans fail simultaneously (0.1/8) 2 = 1.6 x10 - 4 /yr L10 life = 70,000 hrs (8 yrs)

1.4 E lectronic component failure 5,000/1 ,000 = 5 F ailure of electronics at 1 in 1 ,000. Maximum estimated delivery is 5,000/yr. 1.5 H

- Bridge failure 0.1 H

- bridge failure as 1 in 10 1.6 Sufficiently energetic to ignite 1 Energy liberated is greater than MIE 1.7 Arc in switch 3x10 - 8 From ADL 1991 report 1.8 Sufficient energy to ignite 9.1x10 - 2 From ADL 1991 report

For the	situation	where	a	catastrophic	leak	within	 the	machine	compartment	is	ejected	 from the	VLT	freezer	by	the	fans,	it	is	possible	that	ignition	sources	outside	of	the	freezer	may	ignite the	 mixture.	 According	 to	 ADL,	 citing	 UL	 research,	 a	 release	 of	 refr igerant	 outside	 of	 a refrigerator	is	dispersed	below	the	lower	flammable	limit	in	about	one	minute.	We	will	assume that	the	same	situation	will	apply	to	the	VLT	freezer	when	the	fans	eject	a	flammable	mixture. Again	 we	 are	 assuming	 that	 the	 thermosiphon	 tu bes	 catastrophically	 leak	 in	 the	 last	 thirty minutes	of	delivery.	 In	 this	case,	 the	VLT	 freezer	is	switched	on,	operates	normally	(with	 the exception	 of	 the	 thermosiphon)	 and	 therefore	 discharges	 an	 explosive	 mixture	 into	 the immediate	surrounds	of	its	pla cement	by	the	fans. Ignition	sources	may	be	door	switches,	dry contact	relays,	gasket	heater	relays	and	/	or	other	energetic	sources	in	the	immediate	vicinity
of	the	freezer. A	worst

- case	laboratory	situation	would	have	VLT	freezers	lined	up	next	to	each other,	spaced	 ten	inches	apart.	 It	is	quite	conceivable	 that	an	adjacent	 freezer	could	ingest	a discharge	 of	 a	 flammable	 gas	 mixture.	 We	 will	 assume four additional	 freezers	 in the immediate	vicinity,	operating	normally. Each	freezer	would	ingest	the	charge	and	expel	it	to	its neighbor. We	will	assume	that	the	charge	is	equally	potent	for	each	freezer	but	is	sufficiently dispersed	 by	 the	 fourth	 freezer	 not	 to	 present	 any	 remaini ng	 risk. In	 this	 case,	 the	 ignition
sources	would	be	as	follows:

a. Gasket	 heater	 relay.	 This	 would	 be	 functioning	 in	 the	 adjacent	 VLT	 freezers	 since	 they would	likely	be	at	temperature.	The relay	is	closed	twice	in	every	hour. We	are	including the	relay	here because	they	could	exist	in	non	R

- 170	units.
b. Door	alarm	switch.	The	door	of	an	adjacent	freezer	could	be	opened.

c. Dry	contact	relay.	This	could	be	energized	if	a	fault	is	detected	in	an	adjacent	freezer.Confidential Global Cooling Inc. Page 28 June 2013 Table 6 Failure	Rate	Estimates	for	an	External Event Event Description Frequency of Probability Source / Discussion

2 .1 Sudden release 0.0005/5 = 1x10 - 4 /yr From Table 3

2 .2 Leak occurs at delivery 30/(7 x 24 x 60) = 3x10 - 3 Assume one week for delivery with probability of fault occurring in last 30 minutes 2 .3 Adjacent freezer door is opened Handled as a switch event

2 .4 Adjacent freezer gasket heater relay is energized Handled as a switch event

2 .5 Adjacent freezer dry contact relay is energized Handled as a switch event
2.6 Arc in switch 3x10 - 8 From ADL 1991 report 2.7 Sufficient energy to ignite 9.1x10 - 2 From ADL 1991 report



### 6.4 Fault	Tree	Analysis
Fig.	13 shows	the	fault	tree	for	a	fire	or	explosion	in	the	machine	compartment	for	the	worst

case	 data.	 The	 most	 serious	 ignition	 source	 is	 an	 ene rgetic	 failure	 of	 the	 H

- bridge	 o n	 the
inverter board	 ( see Fig.	 6)

. The	 frequency	 of	 a	 fire	 or	 an	 explosion	 inside	 th e	 machine compartment	is 2.4 x	10

- 1 1 /yr

. under	the worst

- case assumptions.

Fig.	13 Worst	Case	Scenario	for Explosive	Event	in	Machine Compartment 1.0 5 X E-1 2.4 X E-11 /yr

Failure of Electronic Component Causes Ignition

9.1 X E-2 Leak Occurs at Final Delivery

3 X E-8 0.1 Switch Causes Ignition Both Exhaust Fans Not Functioning Sudden Release Leak Ignites

Arc in Switch Sufficient Energy to Ignite H-Bridge Failure Electronic Component Failure Fire or Explosion Inside Machine Compartment

5 0.5 X E-1

5.4 X E-9

2 Switches 1.6 X E-4 /yr 1 X E-4 /yr 3 X E-3

Sufficiently EnergeticConfidential Global Cooling Inc. Page 29 June 2013 Fig.	14 shows	the	fault	tree	for	having	a	fire	or	an	explosion	outside	of	the	VLT	freezer	within	a typical laboratory	space	using	worst

- case	data. Any	of	four	adjacent	VLT	freezers	are	assumed to	 be	 likely	 ignition	 sources	 to	 the	 gas	 cloud.	 The	 ignition	 sources	 are	 assumed	 to	 be	 from switching	events	such	as	relays	and	door	switches.	An	energetic	electronics	f ailure only	occurs on	start	up	so	it	is	not	considered	as	an	ignition	source	in	the	adjacent	freezers. The	frequency of	 a	 fire	 or	 an	 explosion	 caused	 by	 adjacent	 freezers	 is	 1	 x	 10

- 14 /yr

. under	 the	 worst

- case assumptions.
In	 contradistinction	 to	 household	 refrigerators,	 the	 chance	 of	 a	 fire	 or	 explosion	 is much higher	within	the	VLT	freezer	machine	compartment.

Fig.	14 Worst

- Case	Scenario	for	an	Explosive	Event	in	an	Adjacent	Freezer



### 7 R ISK 

### M ITIGATION

Given	t he	risk	of a fire	or	explosion	in	the	machine	compartment	as	2.4	x	10

- 1 1 /yr.	and noting the	 estimation	 of	 the	 currently	 installed	 base	 of	 VLT	 freezers	 at	 500,000 5 the	 potential	 of added	annual	 fires	is	negligibly	small.		Nevertheless,	it	is	prudent	 to	consider	risk	mi tigation measures.	We	believe	that	the	following	items	are	most	likely	to	return	good	results:

1. Check	for	leak	integrity.	We	already	do	this	but	clearly	the	urgency	of	this	task	is	magnified.

5 Internal	estimation Sudden Release Leak Occurs at Final Delivery

3 X E-8 9.1 X E-2 Fire or Explosion Inside Adjacent Freezer Machine Compartment

1 X E-4 /yr 3 X E-3

Sufficient Energy to Ignite Arc in Switch Leak Ignites

3.3 X E-8

9.1 X E-2 3 X E-8 Sufficient Energy to Ignite Arc in Switch Arc in Switch Sufficient Energy to Ignite Dry Contact Relay Causes Ignition

1.1 X E-8

4 Freezers

3 X E-8 9.1 X E-2 1 X E-14 /yr

1.1 X E-8 1.1 X E-8

4 Freezers 4 Freezers Door Alarm Switch Causes Ignition Gasket Relay Causes IgnitionConfidential Global Cooling Inc. Page 30 June 2013 2. Consider	 transportation	 loads	 and	 means	 to	 prevent or	 limit movement	 of	 the thermosiphon	tubes	during	shipping.	The	Unilever	study	also	identified regular movement of	ice	cream	cabinets	in	the failure	of	tubing	joints (Unilever	2008)

. 3. Reduce	 ignition	 sources	 either	 by	 redesign	 or	 by removing	 the	 possibility	 of	 flammable gases	coming	into	contact	with	an	ignition	source (sealing,	 for	example) .	We	believe	 that

we are	 addressing this	 concern	 by	 pre

- testing	 all	 electronic	 components	 used	 in	 the machine	compartment.
4. Conforming	to	UL

- 471	sp ecifically	now	that	this	standard	includes	VLT	freezers.



### 8 D ISPOSAL 

### I SSUES

Safe	disposal	of	discarded	units	must	be	taken	into	account. Currently	there	is	a	framework	to reclaim	refrigerants	 from	VLT	 freezers	at	end	of	life. With	the	use	of	R

- 170,	it	is	vit al	to	alert the	service	or	reclaiming	entity	that	flammable	refrigerants	are	present.	Unless	other	guidance is	 provided,	 we	 would	 suggest	 following	 the	 same labeling requirements	 now	 advised	in	 40 CFR	Part	82	for	hydrocarbon	refrigerants.



### 9 B IBLIOGRAPHY

1. ANSI/ASHRAE. Safety	Standard	for	Refrigeration	Systems. Standard,	Atlanta:	ASHRAE,	2010.

2. Arthur	D.	Little.	"Risk	Assessment	of	Flammable	Refrigerants	for	Use	in	Home	Appliances." Report,	Division	of	Global	Change,	EPA,	1991.

3. ASHRAE. Position	Doc ument	on	Natural	Refrigerants. Report,	Atlanta:	ASHRAE,	2011.

4. Bennett,	Casey. Laminar	Burning	Speed	and	Flame	Structure	of	1,1

- Difluoroethane	(HFC

152A)/Air	and	Difluoromethane	(HFC

- 32)/Air	Mixtures. MSc	Thesis,	Mechanical	and Industrial	Engineering,	North eastern	University,	Boston:	Northeastern	University,	2011.

5. Berchowitz,	D.	M.,	and	Y.	Kwon.	"Environmental	Profiles	of	Stirling

- Cooled	and	Cascade

Cooled	Ultra

- Low	Temperature	Freezers." Sustainability (mdpi)	4,	no.	11	(2012):	2838

- 2851.

6. Carnegie	Mellon	University. Construction	of	Biosafety	Containment	Laboratories. 2007. http://www.cmu.edu/ehs/facilities

- construction/biosafety

- containment

- laboratories.html (accessed	June	23,	2013).Confidential Global Cooling Inc. Page 31 June 2013 7. Holtappels,	K. Report	on	the	Experimentally	Determined	Ex plosion	Limits,	Explosion Pressures	and	Rates	of	Explosion	Pressure	Rise

- Part	2:	Ethane,	Ethylene,	Propane,	n

- Butane,
Ammonia	and	Carbon	Monoxide. Report,	TU	Delft	and	BAM,	TU	Delft,	2002.

8. IPCC.	"Fourth	Assessment	Report:	Climate	Change."	Report,	2007.

9. K aufeld,	M. Availability	of	Low	GWP	Alternatives	to	HFCs. Report,	Environmental Investigation	Agency,	Washington:	EIA,	2012,	53.

10. Kunz,	Oliver. Combustion	Characteristics	of	Hydrogen

- and	Hydrocarbon

- Air	Mixtures	in
Closed	Vessels. Diploma

- Thesis,	Luft	und	R aumfahrttechnik,	University	of	Stuttgart	and California	Inst.	of	Technology,	Pasadena:	Explosion	Dynamics	Laboratory,	1998.

11. Mitu,	Maria,	Venera	Giurcan,	Domnina	Razus,	and	Dumitru	Oancea.	"Temperature	and
Pressure	Influence	on	Ethane

– Air	Deflagration	Param eters	in	a	Spherical	Closed	Vessel." Energy	&	Fuels 26,	no.	8	(2012):	4840

- 4848.

12. NFPA. Standard	on	Explosion	Protection	by	Deflagration	Venting. Report,	National	Fire Protection	Association,	Quincy:	NFPA,	2013.

13. Unilever.	"EPA	Submission

- Use	of	R290	in	Ic e	Cream	Cabinets."	2008.

14. Wikipedia. Adiabatic	Flame	Temperature. June	13,	2013. http://en.wikipedia.org/wiki/Adiabatic_flame_temperature	(accessed	June	23,	2013).