Monitor peak load on three phase 400 amp service

I need to determine the peak load on a 400 amp service. Ideally I’d be able to record every 5 minutes what the current load is and be able to store that to later determine peak. I’d like to monitor the loads for 6 months. The 400 amp service splits off into a 150 amp panel and to 50+ meters before hitting each individual condo breaker panel.

The 400amp service supplies power to 50+ condo units and building common.

Can I use IoTaWatt for this purpose?

This is in Canada.

Thank you !

IoTaWatt will record the average every 5 seconds. From that you can query to get the average for any grouping of those five second measurements, so 5 minute averages are available. There is no capability within IoTaWatt to query the maximum, but you can plot it and see visually the peaks.

If the data is uploaded to a database like influxDB, there are functions within their query do select the maximums.

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I use InfluxDB and have a Flux query to get the maximum, so what you want is achievable. Do you want the instantaneous peak, a 5s average peak, or a 5 min average peak?

I have 5s averages going to InfluxDB and I get the peaks from that. It is easy enough to do more averaging before searching for peaks.

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Thank you!

Can I install it against the three phase service line that is entering the fused disconnect?

Thank you !

The point is to figure out peak load so some hybrid hot water tanks can be installed without blowing the 400 amp fuse to the building and leaving everyone without power. I am looking at having 6 installed eventually. A service upgrade is possible but very costly so as a first step if we have the ability to install a few, achieve some savings and have the peak stay below our service max or look at options to have the tanks avoid running during a certain period of the day that would get the project off the ground. I’ll have to talk to the electrician and see how far below peak we’d want to be with the added load. He didn’t have any experience with three phase energy monitors but it sounds like this will work for my application.

Thanks again !

Okay, that makes sense. I would use the 5s average peak. It is what I am doing for a similar reason. I have automatic standby generator and I wanted to see how much I needed to worry about demand side load management. You need to do the same thing, just at a much larger scale of power values.

Do you actually have a fuse or is it a circuit breaker?

Is it a slow-blow fuse?

I would expect even a 15s overload of 150% to be okay, but at 1min probably not so much. At 5min I would hope the circuit would open to prevent dangerous wire heating.

I suspect your hybrid water heaters are somewhat different from mine. But, even when in efficiency mode (supposed to only use the heat pump) it will turn on one of the elements of the water is too cold. The top element comes on if the top sensor gets below 104°F. The elements also come on if the average tank temperature gets below 65°F (but that is described in the manual). My tank has 4500W elements, so that is a lot more than the heat pump uses at 350-500W.

If you have an unconditioned space that stays over 65°F all year, you can cut the consumption of energy by a factor of 2 or so. If you are paying to heat the space that the HPWH is in the savings will be considerably less.

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It is a fuse. Good question. I don’t know if it is slow blow or not.

I haven’t bought the hybrid tanks yet. They will live in a mechanical room that has a boiler from 1969 which heats up the room as a by product of running so the efficiency should actually be through the roof in the winter when it can recover some of that boiler heat.

It sounds like this will work well. Thank you for the conversation and input !! I assume I just buy the 120v package and get an extra 400amp CT to hook up?

Those look like standard (not time-delay/slow blow) fuses. They probably follow something like this question answers:

Based on that, they are unlikely to cause a problem.

Yes, the base unit is the same. With the US 120V kit you get to choose which CTs you want (at a little discount, so good to figure out what you want to measure beyond the mains). You will need to do some measuring to figure out if the 400A CTs will fit around the multiple wires in your setup.

If you have waste heat, the HPWH is a good deal. I will say that it depends on the cost and what you are paying the heat water now. The standard residential HPWH has an electrical input of 500W to 1KW maximum. If the temperature of the area is above 70°F I suspect they have a higher COP. I think I am getting about 2, but my average temperature is lower. That means I save about $1/day in electricity costs. I don’t know that the HPWH will last the full 10 years of it’s warranty. I doubt it will last beyond it. The warranty is parts only, so it will be interesting to see what happens when it fails hard. After 5 years of no trouble (and the length of the extended warranty I bought) I am starting to have some intermittent failures. Rebooting the water heater has fixed the water heater each time. I am keeping a closer eye on it. I can tell by the power utilization (from Iotawatt) and the temperature information if it is working normal-ishly or not. I can see rust on the supports that hold up the evaporator and the water it outputs, but it is still working. Based on history, it looks like it’s efficiency has dropped some.

I got a good deal on the heater (rebates, etc) and didn’t have to pay much for installation, so it has already been a net positive savings in the first 5 years. Depending on when it fails, I will decide what to do next.

I also have it in series with a larger standard electric water heater. It doesn’t come on, since it gets filled with hot water on a regular basis. If it does come on, I know something is wrong.

Depending on how much hot water you need, you might want to consider getting multiple smaller residential units. I thought about doing that when my standard one dies. I would then put them in parallel, but with automatic valves to only use one at a time.

Thank you !

There are currently two 365,000 btu gas wh units in place. Each gas hwt wholesale goes for about 12k. The gas units have been lasting 8-10 years. One of them is close to year 8 so I figure I can subtract 12k from the cost of the hpwhs and then figure out savings.

I worked backwards from the 365k btu and came up with ~6 hpwhs. I worked forwards from number of units / people as well and came up to a similar number. Really it is more about supplying hot water during peak demand than anything else.

The plan is to put them as inputs to the current gas wh. The service isn’t large enough to support 6 so I am thinking of starting with a couple and setting up iotawatt to determine if I can add more without upgrading the service. The service will likely be updated at some point but the budget will need to be built to do that. In the meantime, we’ll be able to build some experience with the units, work out any issues and hopefully realize some savings. Ideally we’d get the 6 units in place before one of the gas wh and just be able to shut off the gas to the wh and confirm we have no issues. The two gas units are currently hooked up in parallel so even if 6 units didn’t quite make the single replacement and we got rid of one of the gas units I think the combination would still work out. Eventually maybe we replace both tanks. We were looking at the Rheem Proterra 65 Gallon units for $3500 that carry a 10 year warranty but other brands / recommendations would be great.

It is helpful to hear what issues we may encounter with the units as we don’t have any experience with heat pump hot water tanks. I like your setup with the electrical unit which should never turn on - I wondering if there is some way I could monitor the gas tank that is receiving the input water from the hpwh to determine if it has come on.

I’ve ordered the iotawatt kit and some extra CTs so hopefully I can get it to fit. I don’t know if there is much option anyway given I’d need the 400A CTs at the service.

This is what I found for water heaters that size:

That has about a 7gpm recovery rate at a 70°F temperature rise. Two would give you 14gpm continuous usage. Getting that with HPWH will be VERY hard. The equivalent BTU/hr input rate of a HPWH is much, much, much lower than even a regular electric one, let alone a gas one, let alone a high input commercial gas one.

Here is an example. I used to have a 50 gallon direct vent 40KBTU/hr input water heater. With a 20 gallon hot water shower, it would take less than 30 min of burner run time to recover. My electric water heater would take about twice as long. My HPWH takes many hours to do the same thing. The HPWH has an electrical input of 350-500W typically (depends on tank temperature and air temperature). This translates to 1.5 to 5KBTU/hr. The electric elements are about 10X (which is about 15KBTU/hr). Standard gas water heater used to be 40KBTU/hr (probably now about 36K or less). Your commercial heater is 10X that and you have two of them.

The HPWH will use the elements when the tank water temperature gets too cold. Mine turns the top element on when the top is below 104°F and the bottom element on when it is below 65°F. Unless your cold water isn’t very cold (Hawaii perhaps) you will overwhelm a standard HPWH with too much cold water. Usually gas costs less per KWH-equivalent than electricity does. I use propane, so it actually costs similar to electricity, which is part of the reason I went with electric. I got a very large tank to deal with the slow recovery. When I was researching HPWH, I did the math. This is why I kept my old water heater. My HPWH barely keeps up with my usage. I lowered the tank temperature to 135°F and it now gets a rest for about 3 hours a day. If both my wife and I take showers at the same half of the day (instead of one in the morning and one in the evening) the elements are on for at least 30min if not close to an hour. If we spread it out, the elements do not come on.

So, there are definitely efficiencies with a HPWH, but it isn’t really a drop in replacement for your specific needs.

I have the AO Smith HPWH from Lowes. I looked at the Rheem from Home Depot. They looked about the same. The Lowes one was on sale and had better rebates too. The GE one had some serious reliability issues which is why I got the extended warranty. Some of the newer ones have more normal connections at the top. The side connects are more efficient, but they are definitely different and harder to hook up.

I would keep track of how often the water heaters are firing and how much hot water is being used. This is probably not easy to do.