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apartment_guy 05-21-2012 11:40 AM

Concerns re overloading 200 amp service in a 12-unit multi-family
 
I own an older 12-unit apartment building where most of the apartments are served by 60 amp pony circuits. The problem is that the entire building only has a 200 amp service, and with window air conditioners becoming more affordable I worry every time a tenant asks for permission to put one in. For the past two years we’ve had five small (5,200 BTU to 6,000 BTU) window a/c units installed, although I expect that I will be asked to permit more this year. (I am in Toronto, Canada, where we call a “heat wave” anything over 30C (86 F)

Unfortunately my understanding of the principals of electrics is rudimentary. I’ve tried to do a load calculation, but different calculators produce different results, although I am guessing that whatever formula is used I expect that I would find that I am near the max load for a 200 amp service (even without air conditioners).

In practical terms, however, the formula may not produce an accurate picture. It’s quite an efficient building, most of the apartments are quite small (averaging about 450 sq. ft.) and most of the lighting has been converted to CF or (more recently) LED. The twelve apartments average less than 450 sq. ft. (total building size is 7,000 sq. ft.) and only five have electric ranges (three of these being 24” models). There are four dishwashers, but they don’t have heating elements. All of the fridges are EnergyStar or small enough that they consume less than 420 KWH per year. The laundry room has two washers and two dryers (gas fired) but each of these gets about one load per day. On the other hand every apartment has a computer and a microwave oven. Heating and water heating are on gas.

We are on Time-Of-Use metering and I have been downloading daily usage data for two-and-a-half years. I cannot download “peak demand” data except that I can get the peak hourly demand. (I presume that “peak demand” refers to a period of time shorter than one hour).

So far our maximum hourly load has been 8.425 KWH, and this occurred in February of 2011 when I was using heating cables to melt snow.

In the summers of 2010 and 2011 the peak hourly demand topped out at about 6.75 KWH with 5 window air conditioners installed. On July 11th of last year temperatures hit 38.2 C (101 F) and maximum hourly consumption was only 6.6 KWH. This was near an all-time record high for temperatures in Toronto.

So the question is, how many additional window a/c units should I permit (if any?)

AllanJ 05-21-2012 12:58 PM

How many amperes do the air conditioners draw and what voltage (120 or 240) do they use?

With the 200 amp service you have two allotments of up to 200 amps each at 120 volts, or one allotment of up to 200 amps at 240 volts, or combinations thereof.

Load calculations use watered down historical averages to take into account not everyone using their maximum (60 amps @ 240 v0lts per apartment here) draw all at the same time.

Officially you go by the published methods of doing load calculations before you upgrade, expand, or add to the electrical system. If you want to you can estimate amperes drawn by all usage in the apartments and use that to decide how many more air conditioners to allow, assuming you don't need to do any work and don't need to pull any permits.

apartment_guy 05-21-2012 01:06 PM

Quote:

Originally Posted by AllanJ (Post 925790)
How many amperes do the air conditioners draw and what voltage (120 or 240) do they use?

With the 200 amp service you have two allotments of up to 200 amps each at 120 volts, or one allotment of up to 200 amps at 240 volts, or combinations thereof.

Load calculations use watered down historical averages to take into account not everyone using their maximum (60 amps @ 240 v0lts per apartment here) draw all at the same time.

Officially you go by the published methods of doing load calculations before you upgrade, expand, or add to the electrical system. If you want to you can estimate amperes drawn by all usage in the apartments and use that to decide how many more air conditioners to allow, assuming you don't need to do any work and don't need to pull any permits.

Thanks

These are small (5,200 to 6,000 BTU) 110V window units. For new installs I insist that they have an EER of 10.7 or better (that is, EnergyStar-qualified) but most of the existing units are older ones with EERs in the order of 9.7.

Yes, the calculations assume that not everything is running at once (and I've seen multipliers of 35%, 40% and 44% used). Of course, with air conditioners I can imagine that if everyone comes home from work at the same time on a hot summer day then every machine could be running flat out for a while. (Rightly or wrongly, I ask them to turn their a/c off when they are not home, in part to avoid peak-time usage with our time-of-use rates).

apartment_guy 05-21-2012 02:24 PM

Quote:

Originally Posted by AllanJ (Post 925790)
With the 200 amp service you have two allotments of up to 200 amps each at 120 volts, or one allotment of up to 200 amps at 240 volts, or combinations thereof.

Apologies, but I’m not certain what this means, although an electrician told me that I essentially have two 100-amp services. (He also told me that I ought to ensure that the loads are balanced correctly between the two, which makes sense).

Aside from my attempts at load calculations my intuition tells me that a 200 amp service is not adequate for a twelve-unit building. Nonetheless, when I look at my actual usage (which over 2 1/2 years has never exceeded 8.5 KWH) I am less certain. Does 9 KW equate to 82 Amps? (9,000 watts / 110 volts). If so then it would appear that I have some headroom left.

k_buz 05-21-2012 02:33 PM

If you have a 200A service at 240V each leg of the service can handle 200A. So if you have only 120V loads in the building, the service can handle 400A of 120V loads if the loads are balanced between phases.

If you have a 100A service at 240V, you only have 100A on each phase.

If you have 240V loads connected (such as electric ranges) there will be a load on each phase.

As for your exact situation, I cannot comment because I am not familiar with service sizing in Canada. There are a few professionals from Canada on these boards who will be able to give you much more information. If I was forced to give an opinion, it would be that the service is at full load according to calculations.

rrolleston 05-21-2012 03:43 PM

Even the smallest window AC units I have seen usually recommend being on at least a dedicated 15 amp circuit. Because they use about 10 amps of 120. Your service is only allowing about 15 amps of 240 per apartment. That is just barely enough to get by. Not allowing air conditioners could just have them using a bunch of large fans and they draw a decent amount too. I find sometimes it's easier to maintain a temp in a building than at a certain part of the day try to get it cooled down.

Yoyizit 05-21-2012 05:24 PM

You can look up Cooling Degree Days and possibly from your existing data you can figure your average predicted consumption. What you also need to determine is your peak load which can possibly be figured from your high Outside Design Temperature [ODT] , either for 1, 2 or 5 years, for your area.

You may want to move this to the HVAC section.

dmxtothemax 05-21-2012 07:19 PM

First of all make sure all individual units have correct 60a breakers.
Then check that the main breaker is correct at 200a.
This way any overloading will not cause any serious damage.
If you allow A/Cs,
sooner or later they will all have them!
Then there will be problems.
in the short term with only a few it should be ok.
But long term, you will have to upgrade,
as more and more come on line.
Make it clear to every one now!
that the capacity is limited,
and will not serve everyone if they all want A/Cs.

powerfactor 05-21-2012 07:31 PM

Why not just install a 400 amp service and raise the rent???? :thumbup:

Techy 05-21-2012 08:09 PM

Honestly, with just what you have now i bet you could pull 200 amps on atleast 1 leg.



a service upgrade will be needed in the future

rrolleston 05-21-2012 09:17 PM

Quote:

Originally Posted by powerfactor (Post 926002)
Why not just install a 400 amp service and raise the rent???? :thumbup:

I agree this would be the best bet. Eventually you will get someone upset because one tenant will be upset when another has ac and they are not allowed.

frenchelectrican 05-22-2012 12:06 AM

A single service size of 200 amp to run the whole 12 unit IMO that will genrally not fly at all.

It may be ok in old codes era but with modern codes it don't really work that well.

I know my customer have 5 unit apartment and 3 units used window shaker while the other two did have central air ( the rest will upgrade to central air when other three will remodel that time ) and that place have 400 amp service and it really hold up very well with full load I did mesure the load it was only 210 amp max reading with all the A/C's running plus whatever they ran in there.

Note : all the 5 apartments did have 100 amp panels so it was not a issue due the load demand calucation was not high engouh to justify the changeover on service set up to 600 amp size.

Merci,
Marc

goosebarry 05-22-2012 12:18 AM

You might want to look at some example specs for window units. HD is a good starting point.

First to air condition 450 sq ft requires about 10000 BTU using 95F (35C) for the outside temperature.

Energy Star rated (EER 10.7+) units would use 935 Watts or 8.5 Amps (10000 BTU/ 10.7 / 110 V). Currently, normal efficiency units would have an EER of 9.7+ and draw 1030 Watts or 9.3 Amps.

So for 12 units the peak additional draw would be 102 - 112 Amps @ 120V. Overall, you should have adequate capacity. Without knowing the wiring of each apartment, I can't comment on adequacy of the wiring. Ideally, a room air conditioner should be on a its own circuit.

In the US it is very common to include a provision in the lease concerning room A/C.

Lessee provided air conditioners must meet the following conditions:
  • Only temporary window mounted units shall be used. No portable or wall mount units.
  • Maximum of 2 A/C units, not to exceed a combined 10000 BTU.
  • All units must be ENERGY STAR rated (alt: have an EER 9.7 or greater), and less than 5 years old. The ENERGY STAR and EnerGuide labels must remain attached to the unit or a copy provided to management.
  • A/C units must be removed from the windows and windows properly sealed between 1 Oct and 30 Apr.
  • The lesee is responsible for safe and secure installation, including sealing to prevent infestation by pest or vermin.
  • Lesee is responsible for any damage to window, apartment or complex caused by installing or operating a room air conditioner.
Obviously have your lawyer review the woeding.
Here is the link to the Canadian Energy Star page.
http://oee.nrcan.gc.ca/equipment/coo...ntilation/7668

rrolleston 05-22-2012 12:50 AM

That's not too bad. Averages out to about 25 amps per leg with the two 100 amp services if everything is even Allowing 75 amps per leg to be used for other uses.

AllanJ 05-22-2012 07:20 AM

Two 100 amp 120/240 volt services give you four allotments of up to 100 amps of 120 volts each. You (should) have two 100 amp main disconnects which are double 100 amp breakers, next to each other. There may be panels for each of the two services respectively next to each other and with 60 amp main double wide double breakers for each apartment.

Balancing the total load over four 100 amp allotments is theoretically more complicated than over two 200 amp allotments but actually it is preconstrained for better or worse not to be more complicated. Presumably you have six apartments preassigned on each service and ideally the proposed air conditioners, one for each apartment, will be three on each side of the respective service.

You can put an inspection requirement in each air conditioner application. The inspection may include (the details not spelled out to the tenant) your electrician's switching the breaker assignments for the branch circuits in the apartment's panel to make sure the air conditioners for all apartments are balanced on the two legs of the service, after the air conditioner is installed in the chosen window and plugged into the nearest wall receptacle.


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