EcoRenovator - View Single Post - Does cooling your house down at night really save energy?

Xringer · 12-03-10, 06:44 AM

Here's the last 7 hours in weather history, recorded by a station less than 1 mile away.
12/3/10
Current: High: Low: Average:
30.1 °F 30.4 °F 27.9 °F 29.0 °F

The Sanyo ASHP has been set at 21C (69.8F) since yesterday.

It's been 7 hours since midnight and the meter shows 1.8kWh. (38 cents US)
That would be a continuous 257 watts, if it ran without stopping.
(Just a guess, but 257w might generate 3,000 to 4,000 BTUh @29F)..

Can that be right?? It seems way too low for a house built in 1956..

257w x 24h = 6.168 kWh per day..?.

That doesn't jive with data from the last week..
But, it's pretty close to the KWhs from the last couple of days..
date - kWh
12/3 - 11.13
12/2 - 7.52
12/1 - 7.11
11/30 - 7.77
11/29 - 9.52
11/28 - 12.4
11/27 - 11.4
11/26 - 12.4

There are a few things I need to think about..

1. My Den is closed at night. With only a small amount of heat allowed in.

It's 16'x18' and has a lot of glass and poor floor insulation. (No basement out back).
We open the double doors back up every morning, adding more load to the Sanyo..
That might help account for the unusually low over-night power use..

2. At night, the exterior doors aren't being opened and closed..
As opposed to maybe 20 to 30 times during a sunny day.?.
So, no open-door heat loss at night..
(Does open-door heat loss during the day, cancel out our solar gain)?

Edit:
~~~~That was then, this is now. 12/4/2010~~~~

Made one change. One of the double door on the den remained open.

Current: High: Low: Average:
30.6 °F 35.3 °F 30.6 °F 33.8 °F (It's 5F warmer than yesterday)!

At 7 AM KWH = 4.15 (87 cents). (We used 1.8kw yesterday)!

593 watts per hour for 7 hours. (Yesterday, it was 257w per hour).

Den partly open fell to 17.1 C

It was 5deg F warmer outdoors and it took 2.35 kw (49 cents) more power to keep the Den at 17.1C
More than doubled the bill !!

We did bad overall yesterday. Total of 11.13 kw ($2.34)..
Why?? Because it was Netflix night! I cranked up the Sanyo to get more heat in the Den!
I have to admit, it was nice to watch my movie (Get him to the Greek) in a warm Den,
and I new it was gonna cost me.
But I should have looked at the forecast before leaving the den open all night.
We are going to get some solar gain in there this morning..

12-03-10, 06:44 AM	#3
Xringer Lex Parsimoniae Join Date: Feb 2009 Location: Woburn, MA Posts: 4,918 Thanks: 114 Thanked 250 Times in 230 Posts	It's 7AM here in MA USA Here's the last 7 hours in weather history, recorded by a station less than 1 mile away. 12/3/10 Current: High: Low: Average: 30.1 °F 30.4 °F 27.9 °F 29.0 °F The Sanyo ASHP has been set at 21C (69.8F) since yesterday. It's been 7 hours since midnight and the meter shows 1.8kWh. (38 cents US) That would be a continuous 257 watts, if it ran without stopping. (Just a guess, but 257w might generate 3,000 to 4,000 BTUh @29F).. Can that be right?? It seems way too low for a house built in 1956.. 257w x 24h = 6.168 kWh per day..?. That doesn't jive with data from the last week.. But, it's pretty close to the KWhs from the last couple of days.. date - kWh 12/3 - 11.13 12/2 - 7.52 12/1 - 7.11 11/30 - 7.77 11/29 - 9.52 11/28 - 12.4 11/27 - 11.4 11/26 - 12.4 There are a few things I need to think about.. 1. My Den is closed at night. With only a small amount of heat allowed in. It's 16'x18' and has a lot of glass and poor floor insulation. (No basement out back). We open the double doors back up every morning, adding more load to the Sanyo.. That might help account for the unusually low over-night power use.. 2. At night, the exterior doors aren't being opened and closed.. As opposed to maybe 20 to 30 times during a sunny day.?. So, no open-door heat loss at night.. (Does open-door heat loss during the day, cancel out our solar gain)? Edit: ~~~~That was then, this is now. 12/4/2010~~~~ Made one change. One of the double door on the den remained open. Current: High: Low: Average: 30.6 °F 35.3 °F 30.6 °F 33.8 °F (It's 5F warmer than yesterday)! At 7 AM KWH = 4.15 (87 cents). (We used 1.8kw yesterday)! 593 watts per hour for 7 hours. (Yesterday, it was 257w per hour). Den partly open fell to 17.1 C It was 5deg F warmer outdoors and it took 2.35 kw (49 cents) more power to keep the Den at 17.1C More than doubled the bill !! We did bad overall yesterday. Total of 11.13 kw ($2.34).. Why?? Because it was Netflix night! I cranked up the Sanyo to get more heat in the Den! I have to admit, it was nice to watch my movie (Get him to the Greek) in a warm Den, and I new it was gonna cost me. But I should have looked at the forecast before leaving the den open all night. We are going to get some solar gain in there this morning.. Last edited by Xringer; 12-04-10 at 06:37 AM.. Reason: added next day data.