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I appreciate the opinion and I agree, to an extent, that the off peak price hike would certainly discourage large amounts of off peak energy usage in general whether pre-cooling or otherwise. However on the Saver Max plan, the off peak went from .0475 to .0523 which would be $4.80 difference for 1000 kWh. If by pre-cooling I can avoid on-peak kWh's at .08683 and increased demand, and keep me overall more comfortable then it may still be a winner.
I'll have to do a few experiments to be sure. I doubt the pre-cooling would last more than 3 hours before it reached the set temperature, however I don't agree that keeping it at 78 vs 83 is only a few bucks difference and it would certainly jack up the demand. Also I would argue that it is far less wear on the unit to start up once and run for an hour and then not run for the next 3 hours vs starting and stopping 15 times in those same 3 hours.
The way you mention demand I'm not entirely sure you understand how that is calculated. Not trying to be insulting here so please don't take it that way. Your demand is calculated based on the highest single usage at once, so all appliances running at the same time. Your AC unit's demand is the exact same if it is set at 60 or 100 there is no difference in how much electricity it is using in any given minute while it is on. So your demand for the month can be set if your AC kicks on one day in the entire month for 5 minutes or if it running 24/7 the demand is the exact same for that one appliance, lets assume absolutely nothing else is using electricity for simplicity. As far as demand is concerned 78 and 83 mean nothing if it turns on once during peak hours at 83.
The real issue with demand rates is around cooking dinner since those appliances have huge bursts of energy usage, microwave and oven, and add a lot of heat to a house causing the AC to turn on at the same time. Lets say you decide to make a roast for dinner so you turn the oven on to heat up and you turn a burner on at the same time to brown roast in a pan before it goes into the over. You may even microwave some frozen vegetables for a side and while cooking you are in and out of the fridge getting everything you need to cook with. Your oven heating up and a burner on is now your monthly demand plus the microwave usage and the fridge has heated up from being opened so that turns on and now you are running 4 high demand appliances at once setting your demand for the entire month. Add your AC onto that because that oven heats up the house and you are easily at a demand rate of 10 or more for the entire month based on one dinner, and it only gets worse if you had used hot water to wash some dishes or something before cooking the hot water heater is still on. This nightly routine for most households (I'd assume but who knows) is the target of APS with demand rates.
If you want to cut demand costs your AC temp isn't a very effective way to do that since it's electricity usage is static while on no matter the setting the only thing the temp difference does is change how often it turns on and how long it runs while on but neither of those will effect your demand rate. More reliable and cost effective ways to manage demand is to turn the AC off completely while cooking so it doesn't turn on when the oven/microwave are on, manage oven and microwave usage if possible so neither is running at the same time, wire in a timer to your hot water heater is a minor way to cut demand but with the new rates would probably only take 1-3 years to return its cost in savings (they don't use a ton of electricity at any one given time but they do use a lot over the year and we have hot pipes in the summer anyway so it doesn't really need to be on all day), and don't run small appliances during peak hours (coffee makers, stand mixers, etc.). For summer demand if you manage everything right the lowest demand rate you are going to see is probably a 6-8 which is your basic electronics (TVs, computers), fridge, and AC all at once. You can't predict when the fridge is going to turn on (it is 53 outside at 8 am with all my windows open and my 3 year old fridge is running as I write this post) so you will inevitably have the fridge and the AC on together at some point during the month. Didn't mention the dishwasher or laundry because no one who watches their electricity usage so much that they keep their house at 83 will have them on during peak hours anyway.
As for wear on the AC unit itself they are designed to turn on and off repeatedly. Running it for hours on end as people do when pre-cooling can cause excessive moisture build up on the coil and that moisture will freeze (picture below of a 4 year old unit completely ruined in a rental where the tenant has been for 6 years and they used to pre-cool to 68). Over time that can cause corrosion on the coil, especially on the outsides where the piping is larger so there is more area for moisture to collect on. That corrosion will causing the rusting shown and will lead to a coolant leak which will cause the AC to run longer since it isn't blowing as cold and eventually stop cooling altogether. A similar problem occurs when the filter isn't changed regularly enough, lack of proper airflow causes odd suction so the condensate stays on the coil instead of dripping off. A cheap coil replacement is probably $1500, the one in the picture cost me $2200 last year (again on a 4 year old unit).
The way you mention demand I'm not entirely sure you understand how that is calculated. Not trying to be insulting here so please don't take it that way. Your demand is calculated based on the highest single usage at once, so all appliances running at the same time. Your AC unit's demand is the exact same if it is set at 60 or 100 there is no difference in how much electricity it is using in any given minute while it is on. So your demand for the month can be set if your AC kicks on one day in the entire month for 5 minutes or if it running 24/7 the demand is the exact same for that one appliance, lets assume absolutely nothing else is using electricity for simplicity. As far as demand is concerned 78 and 83 mean nothing if it turns on once during peak hours at 83.
Hi AZ Manager,
Thanks for a great explanation around demand rates and AC units. In a way it's kind of tragic that a great family routine -dinner together- is targeted for higher prices. So many families don't do dinner together anymore and it's a marker of dysfunction (not a law, a correlation). My wife will not change her routine under no circumstances.
The way you mention demand I'm not entirely sure you understand how that is calculated. Not trying to be insulting here so please don't take it that way. Your demand is calculated based on the highest single usage at once, so all appliances running at the same time. Your AC unit's demand is the exact same if it is set at 60 or 100 there is no difference in how much electricity it is using in any given minute while it is on. So your demand for the month can be set if your AC kicks on one day in the entire month for 5 minutes or if it running 24/7 the demand is the exact same for that one appliance, lets assume absolutely nothing else is using electricity for simplicity. As far as demand is concerned 78 and 83 mean nothing if it turns on once during peak hours at 83.
The real issue with demand rates is around cooking dinner since those appliances have huge bursts of energy usage, microwave and oven, and add a lot of heat to a house causing the AC to turn on at the same time. Lets say you decide to make a roast for dinner so you turn the oven on to heat up and you turn a burner on at the same time to brown roast in a pan before it goes into the over. You may even microwave some frozen vegetables for a side and while cooking you are in and out of the fridge getting everything you need to cook with. Your oven heating up and a burner on is now your monthly demand plus the microwave usage and the fridge has heated up from being opened so that turns on and now you are running 4 high demand appliances at once setting your demand for the entire month. Add your AC onto that because that oven heats up the house and you are easily at a demand rate of 10 or more for the entire month based on one dinner, and it only gets worse if you had used hot water to wash some dishes or something before cooking the hot water heater is still on. This nightly routine for most households (I'd assume but who knows) is the target of APS with demand rates.
If you want to cut demand costs your AC temp isn't a very effective way to do that since it's electricity usage is static while on no matter the setting the only thing the temp difference does is change how often it turns on and how long it runs while on but neither of those will effect your demand rate. More reliable and cost effective ways to manage demand is to turn the AC off completely while cooking so it doesn't turn on when the oven/microwave are on, manage oven and microwave usage if possible so neither is running at the same time, wire in a timer to your hot water heater is a minor way to cut demand but with the new rates would probably only take 1-3 years to return its cost in savings (they don't use a ton of electricity at any one given time but they do use a lot over the year and we have hot pipes in the summer anyway so it doesn't really need to be on all day), and don't run small appliances during peak hours (coffee makers, stand mixers, etc.). For summer demand if you manage everything right the lowest demand rate you are going to see is probably a 6-8 which is your basic electronics (TVs, computers), fridge, and AC all at once. You can't predict when the fridge is going to turn on (it is 53 outside at 8 am with all my windows open and my 3 year old fridge is running as I write this post) so you will inevitably have the fridge and the AC on together at some point during the month. Didn't mention the dishwasher or laundry because no one who watches their electricity usage so much that they keep their house at 83 will have them on during peak hours anyway.
As for wear on the AC unit itself they are designed to turn on and off repeatedly. Running it for hours on end as people do when pre-cooling can cause excessive moisture build up on the coil and that moisture will freeze (picture below of a 4 year old unit completely ruined in a rental where the tenant has been for 6 years and they used to pre-cool to 68). Over time that can cause corrosion on the coil, especially on the outsides where the piping is larger so there is more area for moisture to collect on. That corrosion will causing the rusting shown and will lead to a coolant leak which will cause the AC to run longer since it isn't blowing as cold and eventually stop cooling altogether. A similar problem occurs when the filter isn't changed regularly enough, lack of proper airflow causes odd suction so the condensate stays on the coil instead of dripping off. A cheap coil replacement is probably $1500, the one in the picture cost me $2200 last year (again on a 4 year old unit).
A little bit TL : DR but I wanted to point out that with APS, Demand is not measured at the highest point during the month, its actually measured over an entire hour and resets every hour on the hour. So it doesn’t matter if you have your AC, dryer and oven all running at the same time, or if you have your AC run for 20 min, your dryer for 20 min and your oven for 20 min, your Demand will be the same. With APS, your Demand is essentially the same as your highest one one hour of electric usage for that month, during on-peak hours.
My AC hasn't been on since the end of October and the (gas) heat won't be on until the end of December if it ever actually cools down.
I dont know how people do this honestly - does the AC literally not turn on, or you manually turned it off?
We leave ours at the same temp all year, 77º for cool and 72º for heat (Nest themostat that can be set for both cool and heat at the same time) and the AC has been turning on daily. I just looked at the history now in th app and the AC ran for 3 hours yesterday (I think we did have it a bit lower as some guests were over), 30 min the day befor, 30 min day before that, 1.5 hours day before. In the past 10 days, there was only one day that the AC did not turn on for at least 30 min.
I should probably add that we never open the windows though, took off all the screens (hate the non clear view with screens on the windows).
I dont know how people do this honestly - does the AC literally not turn on, or you manually turned it off?
We leave ours at the same temp all year, 77º for cool and 72º for heat (Nest themostat that can be set for both cool and heat at the same time) and the AC has been turning on daily. I just looked at the history now in th app and the AC ran for 3 hours yesterday (I think we did have it a bit lower as some guests were over), 30 min the day befor, 30 min day before that, 1.5 hours day before. In the past 10 days, there was only one day that the AC did not turn on for at least 30 min.
I should probably add that we never open the windows though, took off all the screens (hate the non clear view with screens on the windows).
It is manually turned off and the windows are open. Little warm inside today while cooking but nice overall still.
Side question for you HX_guy, one of my neighbors has been saying that your company is owned by Sunrun, is that true?
A little bit TL : DR but I wanted to point out that with APS, Demand is not measured at the highest point during the month, its actually measured over an entire hour and resets every hour on the hour. So it doesn’t matter if you have your AC, dryer and oven all running at the same time, or if you have your AC run for 20 min, your dryer for 20 min and your oven for 20 min, your Demand will be the same. With APS, your Demand is essentially the same as your highest one one hour of electric usage for that month, during on-peak hours.
I'm not sure that I understand your post completely, but if you are thinking peak demand is instantaneous use this is incorrect. It makes a difference both what you use and HOW LONG YOU USE it. A huge difference. The whole enchilada, because usage is averaged over the hour. My peak in winter is usually 2 or less and my ac runs often either for heating or cooling, but it does not run very long. In summer it will run flat out for an entire hour in August and peak demands in August are around 7. Anyway, here is an explanation from APS. I may have linked this earler, so apologies if that is the case:
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but I wanted to point out that with APS, Demand is not measured at the highest point during the month, its actually measured over an entire hour and resets every hour on the hour. So it doesn’t matter if you have your AC, dryer and oven all running at the same time, or if you have your AC run for 20 min, your dryer for 20 min and your oven for 20 min, your Demand will be the same. With APS, your Demand is essentially the same as your highest one one hour of electric usage for that month, during on-peak hours.
