New Heat Pump with Peak Power Pricing
Seems the world of how power is priced is starting to change. Utilities want to put off building new power plants and buy expensive power on the spot market so Oklahoma Gas and Electric is offering. about 1/2 off the normal rate except between 2 and 7 pm M-F. Between 2 and 7 the price goes between the 1/2 off rate and about 4.5 times the normal rate. The hotter it is the higher the price.
Right now the program is voluntary and it saved me about $200 bucks last month but I think given the fact that the power industry is not spending billions installing smart meters to help out their customers I think we are going to see a move towards VPP on a mandatory basis.
Right now the upstairs has a 2.5 ton for about 1100 sq feet with expanding foam in the walls and above the drywall. The air handler is in the attic.
The 7 hours it takes to reach 78 is really not good enough.
Here is what I am thinking about.
1. Oversize it big time (5T) so that we can deal with the heat that is trapped up there.
2. Go with a 5T 2 speed unit. Anyone making a ducted inverter system?
3. Go with a 3T and keep the 2.5T as a "helper" to be used for an hour or two to get rid of the trapped heat.
4. Buying and 40 ton chiller on ebay and turn and cool things down in 5min (just kidding)
Looking for your input.
Check for and fix any duct leakage.
7 hours to get to 78 from what temp?
About 92 or 93. I don't have any leakage and I had the system checked. They cleaned the evap and said the pressures were all fine. The air coming out is cold.
I too am on the OG&E Smarthours program. Your thermostat should be programmed to precool your house between 12-2 while power is at 4.5 cents, I have mine set to 72. House doesn't get hotter than 81 during peak hours. If you don't already have a programmable stat, OG&E will give you one for free including installation. 7 hours for a cool down to 78 is reasonable when the start temp is in the 90's.
Yes, we do this and I am getting the same results on the lower floor, the upper floor however is just beastly and I have resorted to setting the tstat at 90 and it seems to get there about 6:30 or so the last few days.
I am guessing that between the roof, walls, what comes up from the lower floor and all the windows I have up there it's really hard to keep the heat out.
I guess I could blow in a layer of fiberglass over the 6" of open cell foam I have in the attic and see if that helps me.
I don't really care all that much how out it gets up there at that time of day because nobody is really up there, however i really need it cooled off by the 9 or 10 for sleeping and it is still about 85 or so at that time of day.
Are you setting 90 as you base temperature? If you have a Smarthours thermostat it will add up to 5 degrees to your set point making it actually 95 up there. Try 80 with conservation mode between "balanced" and "savings". This will make it 80-89 from 2-7 depending on price. Setting your stat lower from 2-7 is a lot cheaper than a new HVAC system. Also replace your roof with a lighter color the next time we get one of those Oklahoma hailstorms. Add more attic ventilation, most attic are seriously under ventilated. If your attic is more than 130F @ 4pm, more venting is needed.
A 3 ton 2-stage might help a little without compromising comfort. I agree with more attic venting and checking for duct leaks.
Precooling is probably the best option. But it's effect will be limited in a smaller home since they heat up and cool off a LOT faster than a larger home.
Overall I'm not a big fan of setbacks. When you go to recover at 7PM, you AC unit will be about 20% less efficient than it was on average all day until that point, especially with a 2 stage unit.
I hope they never force us into time of use pricing here. It will be a while I think. It's optional now, but they charge you about $10 extra on you bill each month for the "privledge".
Motoguy, OG&E is pushing for VPP pricing. The meter required to do it is already installed so no extra charge. Most people switching to it are saving 25% on their power bills. Most utilities will switch to some type of TOU plan eventually in order to reduce blackouts/brownouts. The theory is let those who use the most power during peak demand times pay for the infrastructure upgrades.
Yes there is some efficiency loss due to the higher temps @ 7pm, but there are no cycling losses which more than makes up it. Figure a central A/C takes 5-10 minutes to get pressures stabilized, at which time it's not running at peak efficiency. When it runs for hours at a time pressures are stabilized the whole time.
Last edited by 54regcab; 07-22-2012 at 10:03 AM.