How many air-cons/water heaters per 15/45A phase?

[simon43]

My small hotel is located on a rural road in Phuket with a 3-phase, 15/45 electricity supply.

Usually, when constructing a guesthouse or hotel, the electricity company stipulate that a transformer must be installed, (as they did for my first hotel). For the current demand of my hotels, this transformer cost is at least 500,000 baht.

But when I built my last 2 hotels on this small road, the head of the electricity company said that I wouldn't need to install this expensive transformer, so long as I didn't 'overstress' the electricity supply!

So that was all fine and I saved 500,000 baht.

During construction, I wired my hotel rooms to equally share out the current demand, so that the 3 phases were generally balanced in what they had to supply to meet the current demand.

I wired 2 guest rooms per phase, and each guest room has an air-con, instant hot water heater (3KW), and then the low demand TV, lights etc, plus a potentially-higher current demand from a hair-dryer.

Now I really need to build some more guest rooms to meet the high number of bookings, but I am not sure if I can build air-con rooms with their air-con units and instant hot water heaters, and not 'blow' the electricity supply.

I have a clamp meter, so can do a steady-state, current-demand measurement on each phase by switching on everything in the rooms and measuring the current drawn.

But what about the start-up current demand when the air-con and water heater are switched on? How can I estimate this?

Furthermore, I understand that a 15/45A supply means that the current available is between 5 and 45A, but no guarantee of what the actual value will be that the system can support.

So with the additional guest rooms, I want to wire a total of 3 air-cons and 3 water heaters and 3 'general' electrics onto each phase.

Will this work or will there be smoke???

[lopburi3]

Such meters are normally on a 50 or 63 amp main breaker so as long as peak does not exceed that for any period of time should be OK.

I have a home with 9 residents and 5 air conditioners (all would only be used late at night - obviously in hotel that would not be the case) and 5 refrigerators and 5 - 3.5kw heaters and have never had and issue with single 15/45 service on 63 amp main breaker.

[Forkinhades]

Also your MCBs for your final circuits can handle 10 x nominal current for a short period of time, which can handle any start up currents that you might have.

Just use your clamp meter to find running currents.

[simon43]

I have a home with 9 residents and 5 air conditioners (all would only be used late at night - obviously in hotel that would not be the case) and 5 refrigerators and 5 - 3.5kw heaters and have never had and issue with single 15/45 service on 63 amp main breaker.

Good Heavens! In that case, I have been far too cautious with my air-con allocations per phase.

In that case, I think I will build another dozen or so air-con rooms....

Typo correction for my first post, I meant to say 'Furthermore, I understand that a 15/45A supply means that the current available is between 15 and 45A'

Edited December 20, 2015 by simon43

[lopburi3]

Just remember that you will likely have A/C running in multi rooms during the hottest part of the day - where as I only run one 9k BTU unit normally during the daytime. But I do have the refrigerators running plus a water cooler so that pulls a lot of power during hot season and they are not in air conditioned areas.

[Crossy]

What size A/C and water heaters do you have / intend installing?

What size is your current main breaker?

If we assume a 3.5kW shower and a 12,000 BTU A/C we're looking at a peak running consumption of about 4.7kW (about 20A) per room, giving us 2 rooms per phase.

But we can safely assume that not everyone will shower at the same time and all the A/C compressors will not be running together so we can double that (or even more).

You should be able to run 4 rooms per phase without the supply flinching.

The main breaker will protect the meter anyway so the worst that would happen would be everything goes off.

EDIT What you really want is a peak demand meter. You could do worse than a 3-phase energy meter ( http://www.currentcost.com/product-envir.html ) with two extra sensors (so you have one on each phase) and some free software (Tektoniq Energy Station is free for a month and will do what you need).

[Forkinhades]

Can you run 1 new circuit to each new room? This will depend on number of spare ways you have. If you so can you advise of length of runs, and give us the ratings of your equipment. Crossy will do the math for you, and apply diversity.

[simon43]

But we can safely assume that not everyone will shower at the same time and all the A/C compressors will not be running together so we can double that (or even more).

Unfortunately, that is not a given.

This is an airport transit hotel. From about 9am until 7pm, there are no guests. Then they all start to arrive, sometimes all within a short timeframe, sometimes throughout the night. Almost all guests use the air-con all night. Guests will shower, (3KW) heaters, but I cannot foretell if they all shower at the same time. Interestingly, (and this is not a swipe at my Chinese guests), the vast majority of my Chinese guests never take a shower.....

The air-cons are 9,000 BTU ==> small because I build the rooms with mesh windows front and back (no glass), to allow a free flow of air, and there is also a ceiling fan that works well.

I will do some current measurements first, (and I'll check out that link to a peak demand meter).

I could reduce the current demand per room by changing the instant water heater for a solar water heater. But that costs about 20,000 baht per room and I'm left with a batch of instant water heaters to try to sell off.

[Crossy]

Reducing the A/C too 9,000 BTU will give you a bit of leeway.

How many rooms in total do you anticipate having? Any kitchen or other heavy draw stuff?

There is also the possibility of upgrading your supply to a 30/100 3-phase if it's available in your area.

EDIT What value (Amps) is the current main breaker?

[simon43]

How many rooms in total do you anticipate having

If I build them, then I can fill them The airport is always very busy. I have built 4 small hotels so far in this locality (total = 37 guest rooms) and they are all usually full every night of the year.

The kitchen has a deep fat fryer and 3 toasters - those are the primary heavy users of electricity.

Upgrades of the supply to 30/100 is not avalable on this small road in the rubber trees.

Main breaker is indeed, 63 amps.

[Crossy]

Your 63A incomer, assuming it's a C curve (most seem to be in Thailand) will carry 90A for about 15 minutes before tripping, it will handle 75A 'for ever' (the graph stops at 10,000 seconds). The meter won't mind either.

Whilst I wouldn't recommend running constantly in the 63A+ zone the occasional foray towards 90A (4 rooms simultaneously taking a shower with the A/C blasting per phase) is going to cause no issues.

I would suck-it-and-see, I would be more concerned about the supply voltage drooping on max load.

[simon43]

I would be more concerned about the supply voltage drooping on max load.

The supply voltage goes up and down already with the load, dropping at times down to 190 volts. (The road transformer is maybe 1Km away).

This doesn't cause any problems - one can hear the air-con unit sound change in tone as the voltage varies and the filament lights dim a bit.

I remember opening my first hotel with 4 air-con rooms when it was still only connected to the single phase building supply - the lights dimmed down to candles when the air-cons started up

Update: To measure the current situation (meaning in time, not in amps!), I just purchased off Ebay a wi-fi current meter and 3 current transformers. I can clamp the transformers onto my supply cables and then put the display meter on my desk... and watch what happens over a typical 24 hour period.

Edited December 20, 2015 by simon43

[lopburi3]

You might also replace some of those lights - will save electric and provide full lighting even at that 190v or lower. Should be cost effective as normally they last a very long time and warm white is now easily available if that is a concern..

[Forkinhades]

Wifi current meter, oh I like that, link please

[Forkinhades]

Your 63A incomer, assuming it's a C curve (most seem to be in Thailand) will carry 90A for about 15 minutes before tripping, it will handle 75A 'for ever' (the graph stops at 10,000 seconds). The meter won't mind either.

Whilst I wouldn't recommend running constantly in the 63A+ zone the occasional foray towards 90A (4 rooms simultaneously taking a shower with the A/C blasting per phase) is going to cause no issues.

I would suck-it-and-see, I would be more concerned about the supply voltage drooping on max load.

Agree to suck and it and see, and with your wifi monitors it will be very helpful.

Any inductive loads (ie motors), have an in rush current for 2 - 6 seconds, then should settle down to normal running current after this period. C curve type MCBs can handle 10 x nominal current for 1 second, and 5 x nominal for 4 seconds. So if your Chinese visitors turned on everything at once your main MCB will handle any inrush.

Too many different variables to determine exactly, so this is where your wifi monitoring will be priceless.

[simon43]

Here's the link:

http://www.ebay.com/itm/261699044418

I can sit the display on my desk and the transformers/wi-fi tx unit sits near to my 3-phase input cables, about 15 metres away.

[Crossy]

Ah, it's a wireless energy monitor similar to the CurrentCost unit I linked to earlier, shame it doesn't appear to be able to link to a PC.

Should do the trick but not quite what I expected.

[itsmylife]

Change to LED lighting more $$$ save for you .

[RichCor]

Here's the link:

http://www.ebay.com/itm/261699044418

I can sit the display on my desk and the transformers/wi-fi tx unit sits near to my 3-phase input cables, about 15 metres away.

Not WiFi, at least not by the description.

The wireless transmitter uses 433MHz, a frequency range used in most countries for license-free Low Power Devices, and licensed HAM Radio operations.

Just saying.

[casualbiker]

Why not change the showers out to gas showers?

[lopburi3]

Why not change the showers out to gas showers?

What could go wrong with that? As someone who had to use shower gas heaters before electric type was available here can only shake my head - not only did I have to block most jets to keep the water from scalding - and vent to avoid suffocation - and maintain gas line in a country where gas is not used in home type environment.

[casualbiker]

Dunno. I used one at a resort.. Seemed OK.. It did get hot.. But was controllable.. Ventilation would obviously be required.

[harrry]

Not sure this is legal or doable but could you when you add the new rooms do them as completely seperate units. Obtain a seperate supply for them the same way as we have for the three houses on our property.

Then you could have another 15-30 available and no problem

[harrry]

Why not change the showers out to gas showers?

What could go wrong with that? As someone who had to use shower gas heaters before electric type was available here can only shake my head - not only did I have to block most jets to keep the water from scalding - and vent to avoid suffocation - and maintain gas line in a country where gas is not used in home type environment.

Definitely dangerous in a hotel..... probably dangerous in a house,.

[casualbiker]

Why not change the showers out to gas showers?

What could go wrong with that? As someone who had to use shower gas heaters before electric type was available here can only shake my head - not only did I have to block most jets to keep the water from scalding - and vent to avoid suffocation - and maintain gas line in a country where gas is not used in home type environment.

Definitely dangerous in a hotel..... probably dangerous in a house,.

not if properly vented.

[lopburi3]

It is a lot more than venting - you have to store the gas, you have to deliver the gas to unit, you have to ignite the gas. Each step presents additional concerns and dangers (especially in a small hotel without much supervision).

[harrry]

Why not change the showers out to gas showers?

What could go wrong with that? As someone who had to use shower gas heaters before electric type was available here can only shake my head - not only did I have to block most jets to keep the water from scalding - and vent to avoid suffocation - and maintain gas line in a country where gas is not used in home type environment.

Definitely dangerous in a hotel..... probably dangerous in a house,.

not if properly vented.

Even piped gas is not allowed in multistory buildings in most parts of Australia because of the risk of gas pooling and explosion. I know they are safe if you know what you are doing...and are very well maintained however this does not apply when the person who is using them is unfamiliar with them.