ISY and Peak Metering

[JimMc]

Our local power company is moving to a peak metering scheme for setting consumer billing rates. Customers will be billed on a combination of 1) their overall monthly usage (kW-hr), and 2) their peak load during the billing cycle.

The house has two roof-mounted A/C units with separate thermostats and these together are the main use of electricity. If both units were to start/run at the same time it greatly exaggerates the peak electrical load and will jack up our bills.

Are there any working & debugged methods (we already have a ISY control for lighting) to sequence the two A/C units so that only one can start and run at the same time? BTW the power company does offer grid-tied peak demand switching controls, but only for commercial accounts that use at least 3000 kWhr a month.

[Teken]

Hello JimMc,

 

What kind of solution are you looking at simple <~> complicated? What is your budget and how much resources are you willing to invest in this endeavor? Off the top of my head the simplest and direct approach which requires no added costs is to schedule the one thermostats to not operate during these peak periods.

 

To do so will require a compromise in personal comfort or a large investment in the homes superstructure, pre cooling, to load shedding.

 

If your interested in knowing more about any of the above from super structure, passive cooling, pre cooling techniques, to load shedding let me know.

[JimMc]

Hello JimMc,

 

What kind of solution are you looking at simple <~> complicated? What is your budget and how much resources are you willing to invest in this endeavor? Off the top of my head the simplest and direct approach which requires no added costs is to schedule the one thermostats to not operate during these peak periods.

 

To do so will require a compromise in personal comfort or a large investment in the homes superstructure, pre cooling, to load shedding.

 

If your interested in knowing more about any of the above from super structure, passive cooling, pre cooling techniques, to load shedding let me know.

My preferred solution would be a new pair of off-the-shelf thermostats that incorporate enough smarts to implement load sharing. IOW no software or reliance on any networked devices. With more customers facing this peak metering issue it seems some thermostat maker might have a product, but my search so far hasn't turned up anything.

 

The next step is a ISY-based solution to lock out power to one of the units while the other is starting/running. I haven't measured it yet, but I'm guessing the start-up current surge is higher than the current draw when the compressor is running. If it's a 2:1 ratio then it might be OK to have both units operating simultaneously on really hot days as long as both compressors don't start up at the same time.

[larryllix]

Starting two A/C compressors at the same time will not usually affect your peak load on a demand meter.

 

Usually the load is integrated over a 15 minute or 60 minute period average. Two small compressors, having starting surges lasting for less than a minute, should not affect the bill much, if it can even be detected.

 

If only one heating zone is in effect some dual stage thermstats could do your job where it would only run one most of the time and use the other for backup. I doubt this is what you are looking for though.

 

In the old days I wired some pump control panels where each start the pump would switch for even wear and tear on the mechanisms. Then if more pumping was needed the second one would switch in. Mostly the second unit never ran.

 

A simple time sharing contactor to only run one A/C compressor at a time may suffice.

 

If these are large units, Insteon modules may not be capable of handling the startup currents and a contactor would be needed anyway. Two Insteon modules could activate two contactors and program logic could control time sharing between them, even just based on a time schedule to avoid the peak times if the demand metering includes that complication also.

 

With future load sensing better logic could be applied.

 

Just some ideas.

[Teken]

My preferred solution would be a new pair of off-the-shelf thermostats that incorporate enough smarts to implement load sharing. IOW no software or reliance on any networked devices. With more customers facing this peak metering issue it seems some thermostat maker might have a product, but my search so far hasn't turned up anything.

 

The next step is a ISY-based solution to lock out power to one of the units while the other is starting/running. I haven't measured it yet, but I'm guessing the start-up current surge is higher than the current draw when the compressor is running. If it's a 2:1 ratio then it might be OK to have both units operating simultaneously on really hot days as long as both compressors don't start up at the same time.

 

Hello JimMc,

 

Can we get a little more insight about the following as it pertains to your home, lifestyle, and environment.

 

- Where do you live (generally speaking)

- What are the highest temperatures normally seen in your area

- What are the TSTATS set for now for cooling months

- Does your area have high humidity vs low

- How many windows are south facing vs north facing

- How old is the home and what style: Bungalow, Two story, Side by side, etc

- How much insulation is in the attic, walls, etc

- Is there an attached garage and if so is it insulated

- What kind of HVAC system do you have in the home: Central, Isolated, Zoned

- What is the current KWH rate now vs the future rate

- Do you have Z-Wave enabled controller

- Do you have any tools to measure temperature(s) inside, outside, attic

- Does the home have a basement

[JimMc]

Starting two A/C compressors at the same time will not usually affect your peak load on a demand meter.

 

Usually the load is integrated over a 15 minute or 60 minute period average. Two small compressors, having starting surges lasting for less than a minute, should not affect the bill much, if it can even be detected.

 

 

Thanks for those suggestions. It looks like the utility meters they are installing can measure actual peak demand because two of the rate plans have a significant "kicker" add-on charge if a customer exceeds 7 kW draw anytime during peak hours.

 

Here are the four rate plans they will offer to residential customers. Confusing as heck -- I'll have to set up a spreadsheet to compare them.

 

 

Basic

 

Basic Service Charge, per month:

$13 - single phase

$18 - three phase

Energy Charge, per kWh:

Summer (May - Sept)

Up to 500 kWh - 10.20 cents

501-1,000 kWh - 11.70 cents

1,001+ kWh - 12.25 cents

Winter (Oct - Apr)

Up to 500 kWh - 9.87 cents

501-1,000 kWh - 11.37 cents

1,001+ kWh - 11.92 cents

 

 

Peak Demand

 

Basic Service Charge, per month:

$10 - single phase

$15 - three phase

Energy Charge, per kWh:

Summer (May - Sept)

6.98 cents

Winter (Oct - Apr)

6.65 cents

Demand Charge, per kW²:

Up to 7 kW - $8.85

More than 7 kW - $12.85

On-peak hours:

Summer: M-F 3-7 p.m.

Winter: M-F 6-9 a.m. and 6-9 p.m.

Excludes all major holidays

² The maximum one-hour measured demand during the on-peak hours of a billing period.

 

TIME of Use (TOU)

 

Basic Service Charge:

$10 per month

Energy Charge, per kWh:

Summer (May - Sept)

Up to 500 kWh

On-peak - 13.87 cents

Off-peak - 9.85 cents

501-1,000 kWh

On-peak - 14.77 cents

Off-peak - 10.75 cents

More than 1,000 kWh

On-peak - 15.32 cents

Off-peak - 11.30 cents

 

Winter (Oct - Apr)

Up to 500 kWh

On-peak - 10.47 cents

Off-peak - 9.78 cents

501-1,000 kWh

On-peak - 11.37 cents

Off-peak - 10.68 cents

More than 1,000 kWh

On-peak - 11.92 cents

Off-peak - 11.23 cents

On-peak hours:

Summer: M-F 3-7 p.m.

Winter: M-F 6-9 a.m. and 6-9 p.m.

Excludes all major holidays

 

Demand Time of Use (D-TOU)

 

Basic Service Charge:

$10 per month

Energy Charge, per kWh:

Summer (May-Sept)

On-peak - 10.06 cents

Off-peak - 6.03 cents

Winter (Oct-Apr)

On-peak - 6.66 cents

Off-peak - 5.96 cents

Demand Charge, per kW²:

Up to 7 kW - $8.85

More than 7 kW - $12.85

On-peak hours:

Summer: M-F 3-7 p.m.

Winter: M-F 6-9 a.m. and 6-9 p.m.

Excludes all major holidays

² The maximum one-hour measured demand during the on-peak hours of a billing period.

[larryllix]

You have a 1 hour demand integration period according to your posted rates.

A 20 second peak would register 1/180th of the difference between your normsl load and the increase in load.

You would never notice the difference on your bill with residential a/c surges. Running to at the same time would make a difference.

TOU shifting may help keep the bills down though. Simple tou stats will do that just fine.

Sent from a tiny keyboard. Response may be brief.

[Michel Kohanim]

Hi JimMc,

 

Which utility and do they have Smart Meters?

 

With kind regards,

Michel

[JimMc]

Hi JimMc,

 

Which utility and do they have Smart Meters?

 

With kind regards,

Michel

Michael,

 

The utility is Tucson Electric Power. As for the new meters, they are described as "advanced meters", so I assume there are some smarts built in. We received a letter stating that customers who opt out of the update to the new meters will be charged an additional $26/mo.

[larryllix]

Michael,

 

The utility is Tucson Electric Power. As for the new meters, they are described as "advanced meters", so I assume there are some smarts built in. We received a letter stating that customers who opt out of the update to the new meters will be charged an additional $26/mo.

So the demand metering is an optional thing but if you don't select it you will have to increase your bill by $26 per month?

Or is it a discount/savings of $26 to entice you into going to demand metering?

 

What are they labelling the extra $26 as? They dont show it in the rates offerred. The meter for demand metering will probably cost the utility another $50-$100 each so it seems the $26 charge may be the other way for the demand meter vs. a simple residential meter for about $20.

OTOH. it's just another piece of firmware these days.

The utility would usually give estimates of end costing results based on the metering history they already have. If they have your demand profile that is very easy to extrapolate from the hourly consumption they will have gathered for the TOU billing, already implemented.....especially with a 1 hour demand.

 

If you do go with the demand metering, and it is listed a 1 hour averaging of consumption, then you need to know how the hour is determined, as a sliding window hour or a block interval (fix windows)

If it a fixed window (not likely with today's technology) you can peak split where you run your A/C half an hour each fixed window so it only indicates half...LOL Done by many industries in the old days... LOL

 

ISY is your friend!

[KeviNH]

With the two separate AC systems, would one system be a higher priority for occupant comfort than the other?

 

I'd be shocked if there isn't a "peak shaving" commercial control board available to accomplish this?  Seems like the logic could be accomplished with a timer and a handful of relays; basically exclusive-or for the two compressors, plus a mechanism to avoid short-cycling.

[JimMc]

So the demand metering is an optional thing but if you don't select it you will have to increase your bill by $26 per month?

Or is it a discount/savings of $26 to entice you into going to demand metering?

 

What are they labelling the extra $26 as? They dont show it in the rates offerred. The meter for demand metering will probably cost the utility another $50-$100 each so it seems the $26 charge may be the other way for the demand meter vs. a simple residential meter for about $20.

OTOH. it's just another piece of firmware these days.

The utility would usually give estimates of end costing results based on the metering history they already have. If they have your demand profile that is very easy to extrapolate from the hourly consumption they will have gathered for the TOU billing, already implemented.....especially with a 1 hour demand.

 

If you do go with the demand metering, and it is listed a 1 hour averaging of consumption, then you need to know how the hour is determined, as a sliding window hour or a block interval (fix windows)

If it a fixed window (not likely with today's technology) you can peak split where you run your A/C half an hour each fixed window so it only indicates half...LOL Done by many industries in the old days... LOL

 

ISY is your friend!

They are adding the additional $26 monthly fee for customers that opt-out -- as a meter reading charge:

 

"Customers who opt out of using an automated meter will be charged a $26 monthly fee starting in May 2017 to

cover the higher cost of reading and maintaining meters that must be read manually." (https://www.tep.com/news/meters/)

 

Thanks for the tip on splitting the load during the monitored hour .

[JimMc]

With the two separate AC systems, would one system be a higher priority for occupant comfort than the other?

 

I'd be shocked if there isn't a "peak shaving" commercial control board available to accomplish this?  Seems like the logic could be accomplished with a timer and a handful of relays; basically exclusive-or for the two compressors, plus a mechanism to avoid short-cycling.

It's a single-level home so the two units are definitely needed on hot days. I suppose the natural division or priority would be east/west depending on the time of day. I too was hoping to find an off-the-shelf control or thermostat -- nothing so far. All of the so called "smart" thermostats currently on the market are really kind of dumb when it comes to load sharing.

[larryllix]

They are adding the additional $26 monthly fee for customers that opt-out -- as a meter reading charge:

 

"Customers who opt out of using an automated meter will be charged a $26 monthly fee starting in May 2017 to

cover the higher cost of reading and maintaining meters that must be read manually." (https://www.tep.com/news/meters/)

 

Thanks for the tip on splitting the load during the monitored hour .

I don't read it that way at all.

 

The $26 is for customers with their tinfoil hats on afraid of RF radiation making them dumb or causing more brain damage, not for demand opting out customers. Usually governments prevent utilities from forcing the cheaper reading method on some types of people. That's the option to still have a meter that a meter reader has to come out each month and read the meter the old way. $26 is cheap and will likely be increased when many give in to automated readings, keeping the reader off their property and away from their attack dogs.

 

With that, you can select an automatic reading meter, and not be billed on demand, for slightly higher kWh consumption rates. The two options are not related.

 

I may be wrong on this, but I would call and ask questions about one necessitating the other. It doesn't sound right according to what most utilities have done, so far.

[Michel Kohanim]

Hi JimMc,

 

Thank you. I think using the Smart Meter would be the best way for you to get pricing as well as usage information. The main question is whether or not they will allow HAN devices to connect to the meters.

 

With kind regards,

Michel

[apostolakisl]

I have recently considered this for my church.  I have come up with a solution using insteon thermostats that does a round robin type of setup with the thermostats.  The thing is, all thermostats control the air to one big room.  In your case, they are separate parts of the house.  So if you alternate turning on thermostat one for say 30 minutes, then the other for 30 minutes, the area that is off may get uncomfortable.  In my case, all air goes to the same room.  With 5 units, I am either going to run one, two, three, four, or five at the same time taking into consideration the outside temp and the difference between desired temp and actual temp.  I will also consider the read date and might put up with a little bit of less than perfect temp toward the end of a billing cycle if I have managed to keep the kw peak down for the previous 28 or whatever days of the month and only need to tough it out for 1 or 2 more days.

 

You can write a whole series of programs that take into account how far off of desired temp the current temp is for the two areas.  Then give preference to the the one that is more off of desired.  At some point, during the hottest/coldest times, you'll just have to bite the bullet and run both units.

 

Our pricing here is total kwh plus kw peak where the peak is a running 15 minute average.