Thursday, November 29, 2012

New Nest thermostat is up and running!

I received my nest on this posting date and had it up and running in about thirty minutes. Between the technical support and what they send you with the unit, I have to admit it was easier than I had thought!

After I got it to communicate with the internet, the unit downloaded an update and then went into a setup mode that was sort of spooky as it was able to analyze my heat pump to a T. I then went to my computer and accessed the unit online (it works in the cloud) and was also able to set it up on my droid phone so that I can control everything from where ever I happen to be.

Weekly schedules can be easily set up
I was very happy with the simple interface that quickly allowed me to set up a custom schedule that can be changed on a whim. Also, this unit has a learning mode whereby it can figure out your heating and cooling preferences. Pretty neat little package all told.

At some point in the future, I plan to do a post on how well I feel the Nest performs overall.

Update: Well, that point in the future has come! The NEST has turned out to be one of my better purchases. It's performance has been flawless and being able to set up a custom schedule has saved me money - a lot of it! I also like the ability to access it via my smart cell phone.

Tuesday, November 27, 2012

Three day study of temperature versus power use

Click to enlarge
 Here is an interesting chart that depicts indoor and outdoor conditions and the effects of cold temperatures on a 2 stage heat pump that has been set to heat a house to 60F. Auxiliary space heat was used to also heat one room to 71F. This test was part of an ongoing series of experiments to help determine how one could save money during the colder months of fall and winter.Note what happens when the temperature dropped below 35F outside and the heat pump was forced to change over to resistive heating as a result.

Saturday, November 24, 2012

Coming soon – The Nest!

After finishing up some studies concerning the saving of energy during cold bouts of weather, I decided to go ahead and purchase a learning thermostat device called the Nest! I’ve determined that, while I can save significant amounts of money by retreating to one room over the course of a cold spell, I still needed to address the house energy envelope as a whole.

I think the Nest is just the device to fill the ticket as it is not only programmable, but it is also network friendly meaning I can access it via a computer or my smart phone. I plan to write a few posts on this topic in the near future.

Wednesday, November 21, 2012

Where heat pumps end up costing money!

I have a dual stage heap pump that services my home and for the most part it does a great job. That is, as long as the outside temps don’t get much below 35°F that is…

The graph above represents actual data of high and low temperatures taken November 2012. For this far in the month, the temperatures have average spot on to historical averages for the last thirty years; about 47°F. So, in fact, this has been a pretty average month, so far. (The mean temperature standard was taken from the weather service's figures for West Plains Mo. for the month of November and rounded).

Now, take a look at the area I’ve marked in yellow – there were 10 out of the 20 days where the overnight lows got down below 35°F. I took these days and averaged out the kilowatt hours of power that was used for those days and came up with 26 kWh. Next, I took and averaged out the power consumed for the other 10 days where it didn’t get quite so cold and arrived at a figure of 18 kWh! Now, since the heap pump will tend to switch over to resistive heating elements below 35°F, I’m guessing that the difference in cost to me will be about 30% more in terms of the electric bill.I'm also guessing that, for a large part, it doesn't matter as much how warm it is during the daytime as it does how cold it gets at night. It'll be interesting to see what happens during the days when the thermometer never gets above freezing, should we experience that later on in the year.

Over the coming winter, I’ll keep an eye on this and see if it holds true.

Notes: During this period of time, the heat pump thermostat was set at 60°F.

Sunday, November 18, 2012

Night time lows below 35°F put the kibosh on energy savings!

This post concerns the effect of home heating when using a heat pump who’s T-Stat was been set down to 60°F for a home while a small 1,400 watt space heater was employed to heat just one room.

It may be interesting to note that many heat pumps become quite inefficient whenever the outside temperatures fall much below 35°F. It’s at that point that many of these units switch over to resistive heating in order to warm a home. Please read the excerpt below:

Heat pumps are only effective to about 35 degrees. Anything lower than that, and you have to use your emergency heat. The two reasons for this are that when the outdoor air temperature gets too cold, the unit cannot extract as much heat from the outdoor air to keep up with heating demand.

Second, condensation forms on the outdoor unit when it is running. In temps above 32 deg (freezing point of water), the condensation simply drains away from the unit. Below 32 deg the condensation freezes to the coil and blocks air flow. When this happens, the unit must go into defrost mode to clear the ice. During this time the heat pump is not heating your house. It’s heating the outdoor unit to clear the ice.

So, at about 35°F, your heat pump also switches over to a set of resistive heating coils located in the inside furnace. This form of heating is much less efficient and power consumption can soar. My heat pump is a two stage heat pump which can even be less efficient as will be explained below:

A single stage heat pump uses the same rate of transfer at all times during operation.  A dual stage (also called a 2-stage), uses 2 different rates of transfer.  Put simply, these 2 stages are kind of like a “high” and a “low”.  When the desired temperature and measured temperature are fairly close in number, the unit will not need to work as hard, thus using the “low” setting.  In this case, a low rate of transfer is all that is necessary for getting to the desired temperature, so why push it and use more energy than is necessary for the job?  Conversely, when the difference in temperature is high, and the unit needs to change the temperature several degrees quickly, the dual stage heat pump will switch over to the high rate of transfer and more energy will be used to get the job done.

This ability to go from a low setting to a high setting simply means that at the high setting, my house will get warmed more quickly. Useful if it’s really getting cold outside and the unit is struggling to keep up. However, not so good from an energy consumption standpoint!

Let’s see this from the standpoint of actual data. Below is a graph of what happened to the outside temperature during the night of November 17-18, 2012. As you can see, at about midnight the temperature dropped into the freezing range (yellow area of graph).

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 Correspondingly, the heat pump began to kick on into Stage 1 (note it never made it to Stage 2 due to both the low setting for the house proper and the fact that it never got seriously cold outside).Let's now look at the corresponding power graph for that period of time as measured by my TED energy monitor:

Click on to enlarge

All those little spikes represent my small space heater kicking on and off all night long. In spite of how it looks, this little unit did not consume much power as it was heating just a 1600 square foot area (my bedroom). The stage 1 spikes were indicative of the switch over by the heat pump sensor to relatively frequent bouts of resistive heating (5 from 12 midnight to 8AM). Once again, my low thermostat setting for the rest of the house combined with the fact that the lowest low was 27°F. is really what saved the overall situation. Had I been trying to heat the entire home using just the heat pump, the situation would have been much different. Now, take a look at the actual power consumed both before and after the mercury dipped below 35°F.:

Click to enlarge

Wow! There was roughly a 50% increase in the amount of energy consumed (all things being equal) after the drop below 35F. I also noticed a residual effect as the house, once cooled, was reluctant to come back up to a 'normal' reading of 60°F.

Disclaimer: There is no way that the information present here could be construed as scientific. It was presented honestly but be forewarned that the author has absolutely no credentials in the areas of heating and cooling.