I can give you one example for them to consider: UPS systems. They all
use sealed VRLA batteries, and are not vented to the outside.
2nd thing for them to chew on: The Midnite Battery boxes are ETL
listed, and you are installing them to the manufacturer's recommendations.
3rd, your use of article 480 is a well worded defense. You should
convert that to a white paper on the subject! What code section are
they using to justify this?
I agree, you can't allow this precedent to be established. I think you
need some backing from SEIA for instance. If they're going to try and
buck decades of established national practice, they really need to have
a darn good reason, and be ready for a challenge.
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 2/5/2014 7:38 PM, Allan Sindelar wrote:
Wrenches,
I need a bit of help here if you have it. Since 2002 we have installed
somewhere between 30 and 35 systems with sealed batteries installed in
manufactured enclosures, originally Outback enclosures and in recent
years Midnite MNBE enclosures. At least ten of these have been indoors
in one form or another - usually a laundry or mechanical room. Our
battery of choice is Concorde SunXtender. We have only added
mechanical ventilation (Zephyr Power-Vent to outside) if the battery
enclosure itself is sealed. Nearly all of these have been permitted
and inspected systems, and we have never had a problem with the
inspectors. Of course, we always vent flooded systems to the outside,
nearly always using a Power Vent fan.
Now we have. An AHJ failed a system for lack of ventilation, and our
attempts to resolve it have not been effective. The Chief Electrical
Inspector has weighed in, and we are right at the point of filing a
Request for Code Interpretation with the New Mexico Electrical
Division Technical Advisory Panel.
I have not wanted to just add ventilation to pass inspection because
of the precedent doing so is likely to set for future installations.
The GC on the job supports my attempts to push back, as do the
homeowners. The Chief Inspector thinks that the 700 square foot
unheated room in which our system is installed is a bedroom; it's
actually a storeroom for the homeowners' collectible book home business.
My request: please send me documented work by others establishing that
PV systems with sealed VRLA batteries are used specifically because
they are considered safe without venting to the outside. If you know
of good online links, I could use them too. For example, the AHJ asked
for a document stating that the batteries or the enclosure were
specifically approved for this use in an indoor location. I can't -
Midnite battery enclosures are simply listed to UL508A, which is
"industrial control panels" and there's nothing specific to this
application in the standard.
To me this is a common-sense issue, but common sense doesn't cut it
when needing to prove a procedure. Can anyone help?
For what it's worth, or for those Wrenches with too much spare time,
below is the text of the original defense of our installation that I
sent to the AHJ. His response was that he's not an electrical engineer
and this would have to be taken upstairs. For what it's worth, I'm not
an EE either... My frustration is showing, I'm sure.
Thank you for any links, reports or other resources you may be able to
send my way.
Allan
-------- Original Message --------
Mr. [AHJ],
I have done some research as followup to our discussion last week
about battery venting for the [X] job. Here are several perspectives
on the issue:
The NEC Section 480.9(A) states only that "Provisions shall be made
for sufficient diffusion and ventilation of the gases from the battery
to prevent the accumulation of an explosive mixture". At root, you are
questioning whether ventilation of the batteries into the storeroom at
the [X] home is sufficient under worst-case conditions.
The NEC Handbook entries for Section 480.9(A), which are considered as
explanatory support documentation and are not Code requirements,
include two paragraphs that are fundamentally contradictory to each
other. The two read:
The intent of 480.9(A) is not to mandate mechanical ventilation.
Hydrogen disperses rapidly and requires little air movement to
prevent accumulation. Unrestricted natural air movement in the
vicinity of the battery, together with normal air changes for
occupied spaces or heat removal, normally is sufficient. If the
space is confined, mechanical ventilation may be required in the
vicinity of the battery.
This paragraph refers to batteries in general, including flooded
batteries which release hydrogen gas as a normal part of the charging
process. The Handbook section goes on to specifically identify sealed
batteries as being unlikely to release explosive gases:
Although valve-regulated batteries are often referred to as
"sealed," they actually emit very small quantities of hydrogen gas
under normal operation and are capable of liberating large
quantities of explosive gases if overcharged. These batteries
therefore require the same amount of ventilation as their vented
counterparts."
Well, no, not exactly. Valve-regulated batteries may indeed require
the same amount of ventilation, but not for the same purpose or under
the same conditions.
Flooded batteries release hydrogen gas as a normal part of every
charge cycle. While it is unlikely that the hydrogen gas could
accumulate to the 4% concentration to become combustible, given its
natural dispersion, the hydrogen sulfide released with the hydrogen
gas is an unpleasant irritant and is potentially toxic with prolonged
exposure at high concentrations. Because of the normal gassing during
the charge cycle, we always provide ventilation of these gases to the
outside. With sealed batteries, the purpose and intent of ventilation
is not to ensure ventilation during the normal charge cycle, but
rather to ensure the safety of the dwelling and its occupants in the
event of a catastrophic failure resulting in the "worst-case scenario"
of unregulated overcharge. In actual experience, the charge regulator
(from the PV array) and the inverter/charger (from a backup generator
in an off grid home) are the bottlenecks through which all charge
current must pass, and failures invariably occur in an "open circuit"
mode, rather than in a "closed circuit without charge regulation" mode.
Nevertheless, we must accommodate the most hazardous potential
outcome, which would be /unregulated overcharge/ of an /already full
battery/ during periods of /high insolation/ (or the equivalent input
from an engine generator). In order to determine the expected amount
of hydrogen gassing under worst-case conditions, I contacted my
Concorde distibutor,Marc Kurth ofCentex Batteries, LLC inBastrop, TX,
512 308-9002. He in turn spoke with the engineering department at
Concorde Battery, the manufacturer of the batteries used in the [X] PV
installation. Their analysis of calculated gassing and airflow rates
is in the attached pdf document which they provided to us. The
batteries in the [X] PV system are Concorde SunXtender PVX-9150T,
rated 915 amp-hours at the C/24 rate. There are 12 cells in a single
series string of 24 Vnom.
The storeroom in which the PV system is located has interior
dimensions of 19' by 37' by an average of 10' tall, or approximately
7,000 cubic feet. It's a large open space. The room has four Pella
double-hung windows, each rated by the manufacturer at 0.3 cfm
fenestration, or 1.2 cfm for all four. Each exterior door (the third
door to the interior living space is excluded as a conservative
calculation but also adds to overall ventilation) is rated at 0.6 cfm,
for a total of 1.2 cfm for the two doors and 2.4 cfm for the building,
assuming no other openings of any sort, such as for wires or for
natural convective losses due to any other air leakage or roof
ventilation.
The 2,000 watt PV array will provide at most about 65 peak amperes of
DC current into the batteries, for the equivalent of a cumulative
daily total of around seven hours in summer. (The inverter/charger is
capable of feeding 105 amperes into the batteries from a generator,
but by the specific stated preference of the homeowners, the home does
not have a backup generator and does not include the ability to accept
generator AC input.) Assuming the worst case of 75 amperes flowing
unregulated into this 900 ampere-hour battery, this C/12 charge rate
is capable of raising the batteries to 30 V DC, or 2.50 volts per cell
(vpc). The cell voltage will not rise about this level because the
internal resistance of the battery, which increases as the voltage
increases, prevents it. Note also that 75 amperes is a peak current
that could only be maintained at midday during conditions of cold, dry
air when the solar insolation intensity is well above standard test
conditions (STC) of 1,000 watts/square meter, when the sun is
perpendicular to the array. As the sun passes across the sky, the
available output current drops substantially. At a reduced input
current, the maximum vpc drops to around 2.40 vpc (and continues to
drop thereafter) and the maximum temperature also drops, in which case
gassing reduces by a factor of about 20 below the rate at 2.50 vpc.
As an additional factor in our calculations, note that all modern
charge controllers are designed to receive PV input at a higher
voltage and lower current than the nominal battery voltage, converting
this to higher current at the lower actual battery voltage. The
Midnite Classic charge controller in this application works this way.
In a closed-circuit failure of the charge controller's functions, the
higher array voltage and lower current would pass through to the
batteries. As long as the input voltage is higher than the battery
voltage, the batteries will accept current, but additional voltage
does not increase the current into the batteries or the amount of
hydrogen released. Rather, in this case the PV modules, which are
wired as four strings of two modules each, will not exceed the rated
short-circuit of the modules x 1.25 (per NEC for PV source circuits.
With four strings, this is (8.61 x 4 x 1.25 =) 43.05 amperes. This is
less than half of the maximum input current used to calculate
worst-case input (as shown in the following paragraphs), and as such
is unlikely to be sufficient to raise the cell voltage to even the
level calculated.
Per the attached engineering analysis by Concorde, assuming that at a
sustained 2.50 vpc the temperature of the batteries rises to 50ºC
(122ºF), the amount of hydrogen released at a constant current at 30V
DC, or 2.50 vpc, at 50ºC is 5.6 cc/hour/Ah/cell. This converts to (5.6
x 915 x 12 =) 61,488 cc of hydrogen released per hour. Converting
cubic centimeters to the more useful cubic feet, 61,488/21,317 cc/cuft
= 2.17 cubic feet per hour of gas released. This amount is less than
the total fenestration of that room (not including the door to the
living space) of 2.4 cubic feet per minute, or (2.4 x 60 =) 144 cubic
feet per hour of natural leakage to the outside through closed windows
and doors.
To take this one step further, 2.17 cubic feet is 0.031% of the volume
of the storeroom. It would take 30 times this concentration to exceed
1% by volume in an airtight container. 4.1% concentration is the
threshold at which hydrogen gas becomes combustible.
Also at 2.50 vpc, at 50ºC, the airflow required to keep hydrogen
accumulation below 1% is 0.0093 liter/minute/Ah/cell, or [(0.0093 x
915 x 12)/28.32 liters/cubic foot =] 3.6 cfm, or 216 cubic feet/hour.
While this exceeds the default window and door fenestration of 144
cubic feet per hour, it is sufficient to disperse hydrogen. Note that
these batteries are not in a confined space; the batteries are located
in a space of 7,000 cubic feet. Note also that is the threshold for
staying below 1% hydrogen concentration; 4.1% is the threshold at
which hydrogen becomes explosive.
I reviewed our records pertaining to the use of sealed batteries in
residential off grid PV systems and in grid-tied PV systems with
battery backup. We have installed more than thirty such systems,
although the great majority have been installed since 2005. Of those,
I have identified at least nine permitted and inspected systems in
which the batteries have been located in what may be considered
enclosed spaces without ventilation between the interior space and the
outside air. Indeed, several of these are in spaces much smaller that
the Shutt storeroom. This is the first time in which an AHJ has
expressed concern about adequate ventilation of sealed batteries.
In two of these thirty-plus confined interior installations, the
sealed batteries were installed in custom-made sealed enclosures which
were wrapped in sheet plywood with controlled intake ventilation. In
both of these we purposely installed Power Vent battery fans (as we
install in all of our systems with flooded lead-acid batteries) ducted
to the outside as a safety feature to prevent the possibility of
accumulation of gases within the battery enclosure itself. However, in
all of the remaining systems we have used manufactured steel battery
enclosures Listed to UL508A. Ventilation from the cabinet into the
room where it can dissipate has always been considered to be adequate
in these applications.
I believe that I have conclusively established that in a worst-case
scenario, the batteries cannot release enough hydrogen to come even
close to dangerous levels. In practical terms, if a failure were to
occur when the residents were away, the batteries would be permanently
damaged by a failed controller, but no danger exists to the home. If
the residents are present when the failure occurs, they would in short
order smell the "rotten egg" smell of hydrogen sulfide. Following
their noses, they'd find a much stronger smell in the storeroom,
suspect that the batteries were the source, turn off the circuit
breakers on the system (which are readily accessible per NEC) and open
the doors or windows.
The 2011 NEC Hanbook states, as noted above: "If the space is
confined, mechanical ventilation may be required in the vicinity of
the battery." The storeroom at the [X] residence is simply not a
"confined space" as built.
Thank you for your consideration of this defense of our installation
practices.
Allan Sindelar
--
*Allan Sindelar*
_Allan@positiveenergysolar.com_ <mailto:al...@positiveenergysolar.com>
NABCEP Certified PV Installation Professional
NABCEP Certified Technical Sales Professional
New Mexico EE98J Journeyman Electrician
Founder, *Positive Energy, Inc.*
A Certified B Corporation^TM
3209 Richards Lane
Santa Fe, New Mexico 87507
*505 424-1112 office 780-2738 cell*
_www.positiveenergysolar.com_ <http://www.positiveenergysolar.com/>
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