[RE-wrenches] Battery venting issue

[Ray Walters]

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 at positiveenergysolar.com_ <mailto:Allan at 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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