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<div class="moz-cite-prefix">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.<br>
2nd thing for them to chew on: The Midnite Battery boxes are ETL
listed, and you are installing them to the manufacturer's
recommendations.<br>
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? <br>
<br>
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.<br>
<br>
<pre class="moz-signature" cols="72">R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760</pre>
On 2/5/2014 7:38 PM, Allan Sindelar wrote:<br>
</div>
<blockquote cite="mid:52F2F599.4020008@positiveenergysolar.com"
type="cite">
<meta http-equiv="content-type" content="text/html;
charset=ISO-8859-1">
Wrenches,<br>
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.<br>
<br>
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. <br>
<br>
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.<br>
<br>
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.<br>
<br>
To me this is a common-sense issue, but common sense doesn't cut
it when needing to prove a procedure. Can anyone help?<br>
<br>
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.<br>
<br>
Thank you for any links, reports or other resources you may be
able to send my way.<br>
Allan<br>
<div class="moz-forward-container"><br>
<br>
-------- Original Message --------<br>
<br>
<meta http-equiv="content-type" content="text/html;
charset=ISO-8859-1">
Mr. [AHJ],<br>
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:<br>
<br>
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.<br>
<br>
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: <br>
<blockquote> 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.<br>
</blockquote>
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:<br>
<blockquote>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."<br>
</blockquote>
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. <br>
<br>
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.<br>
<br>
Nevertheless, we must accommodate the most hazardous potential
outcome, which would be <i>unregulated overcharge</i> of an <i>already
full battery</i> during periods of <i>high insolation</i> (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<font
face="Times New Roman, Times, serif">,<span style="font-size:
11pt; color: black;"> Marc Kurth of</span><span
style="font-size: 11pt; color: black;"> Centex Batteries,
LLC in</span><span style="font-size: 11pt; color: black;"></span><span
style="font-size: 11pt; color: black;"> Bastrop, TX, </span><span
style="font-size: 11pt; color: black;">512 308-9002. He in
turn spoke with </span>th</font>e 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.<br>
<br>
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. <br>
<br>
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.<br>
<br>
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.<br>
<br>
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. <br>
<br>
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.<br>
<br>
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.<br>
<br>
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.<br>
<br>
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.<br>
<br>
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. <br>
<br>
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.<br>
<br>
Thank you for your consideration of this defense of our
installation practices.<br>
Allan Sindelar<br>
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<p class="MsoNormal"><b>Allan <span
class="SpellE">Sindelar</span></b><br>
<span style="font-size:10.0pt"><a
moz-do-not-send="true"
href="mailto:Allan@positiveenergysolar.com"><u><span
style="color:#000099">Allan@positiveenergysolar.com</span></u></a></span><br>
<span style="font-size:10.0pt">NABCEP Certified
PV Installation Professional<br>
NABCEP Certified Technical Sales Professional<br>
New Mexico EE98J Journeyman Electrician<br>
Founder, <b>Positive Energy, Inc.<o:p></o:p></b></span></p>
<p class="MsoNormal"><span
style="font-size:10.0pt">A Certified B <span
class="SpellE">Corporation<sup><span
style="font-size:7.5pt">TM</span></sup></span><br>
<st1:address w:st="on"><st1:street w:st="on">3209
Richards Lane</st1:street><br>
<st1:city w:st="on">Santa Fe</st1:city>, <st1:state
w:st="on">New Mexico</st1:state> <st1:postalcode
w:st="on">87507</st1:postalcode></st1:address><br>
<b>505 424-1112 office 780-2738 cell</b><br>
<a moz-do-not-send="true"
href="http://www.positiveenergysolar.com/"
target="_blank"><u>www.positiveenergysolar.com</u></a><o:p></o:p></span></p>
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