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jasv · Jun 29, 2005, 07:38 AM

Is it better to keep the temperature in the house, close to the desired temperature all day, or let the house heat up in the summer, only to have to bring it back down when you are on the way home? And if it is better to let it heat up a little how many degrees is optimum, as far as energy savings?

labman · Jun 29, 2005, 08:16 AM

Heat gained through a wall is proportional to the difference in temperature. The warmer the house, the less heat gained. Much of the heat gain is air infiltration. Again, the heat plus humidity gain goes down as the temperature and humidity of the inside air goes up. If you have invested in a programmable thermostat or other control, you may as well keep the system off until just enough time to cool it down for you. Shut off lights and any other sources of heat you don't need for the day. If you are using lights for an occupied look, try fluorescents. The compact bulbs are dropping in price and now fitting any fixture. Every watt of unneeded electricity you use, takes 2 more watts for the A/C to remove.

The reduced cycles should extend the life of the system too.

If you leave pets in the house, you may want to set an upper limit on the temperature, keeping it below 80.

jasv · Jun 29, 2005, 10:01 AM

I appreciate the answer but it created another question.
A couple of years ago the utility company installed (with my approval) something on my A/C that would suppossedly reduce my utility bill. What I have noticed is that my A/C seems to go through more cycles. It rarely stays on for more than 5-10 minutes. Should I ask them to pull it out? Is 5-10 minutes a short cycle or is that OK?

labman · Jun 29, 2005, 10:34 AM

The first step may be to have the electric company verify that is how it is supposed to work. It may be that it uses less electricity that way. However, the frequent stopping and starting can shorten the life of the system. The electric company may be better off installing energy conserving devices than building new power plants and upgrading distribution systems. They do not have to pay for the new A/C.

jasv · Jul 5, 2005, 01:33 PM

Labman,
Thanks for you answer. I took some time and when upstairs to see what they could have added. Here is what I think.
A wire is tapped into the air return duct and a wire is also tapped into one of the AC ducts. Both wires are then somehow connected to the AC thermostat wires. Looks like they are connected to the Yellow (compressor), Greeen(Fan), and Blue (2nd Stage compressor) of the thermostat.

I am guessing that this is somehow bypassing the thermostat when air temp is the same in both ducts?

Have you heard of this before?

Since I recently installed 4 zones with 4 different Tstats can I remove the wires?

As a possibly related issue, I've noticed that the compressor goes off for awhile minutes when I have the tstat set for 78 but the house temp is still 80. Shouldn't the compressor keep running until the desired temp is reached?

labman · Jul 5, 2005, 04:05 PM

The utility's wiring is outside my experience. I guess you could have conditioned air passing from the outlet to the return without spreading out into the room and cooling the thermostat. The 2 temperature sensors could shut the system off to give the air a chance to mix with the room air, and then restart. It is hard to say if you should remove the wires.

The thermostats and thermometers used in home HVAC systems are not that precise and accurate. The new programmable thermostats may read out the same temperature the switching circuit sees, but a 2 degree error is easy in the older ones.