Indiana Evaluation of system using HDD and electric consumption

Any numbers I used in that posting were for illustration proposes only. Your mileage may vary.

What do you cook?

I would flat rate your job.

Mark

 

If your system is running permanently in 1st stage with 20F Outside temp, what you seem to indicate above, that would suggest that the additional 25% the second stage brings get you covered down to 5F-10F without the supplement heat. The rated out put of the TT27 in second stage is 37,200 BTU/hour.
If you compare your data from 1/7/15 with 62 HDD and 147 kWh consumption, and then for 1/8/15 you have lesser HDD (58) and more then twice the consumption. Could wind or the lack of solar gain be the factor? The numbers so far indicate that your system is running fine.


Many times it can be more efficient to spend $100 more in supplement heat compared to installing a 5 ton unit, since the 4 ton runs more efficient the rest of the year, so overall, despite high peaks, you might be savings money.

How is your total annual consumption, and what is your baseline of electrical consumption in the middle of the shoulder month, lets say may + october?

That is more telling than your peak days. Geo is not meant to be most efficient on the peak days.

 

Hopefully I have learned quite a bit since I started this thread.

My HVAC system is located in the attic, and I can clearly hear when the compressor is running. The only way for me to determine whether it is running on 1st or 2nd stage is to look at the lights on the zone control board (which is mounted on the unit in the attic). One or more of my three zone thermostats will show an "aux heat on" message when the auxiliary heat is running.

My best guess is that my system is running almost nonstop in 1st stage when the temperature is in the 30's and there is no solar gain (at night). When the temperature is in the low 20's I would guess that the system is cycling between the 1st and 2nd stages. The aux heat seems kick in for varying periods when the temperature is in the mid teens or below.

I tried to type example kWh and HDD figures in a nice legible table. They didn't post quite so neatly. On 1/6/15 I used 67 kWh for 51HDD. This seems impossibly low. On 1/7/15 I used 147 kWh for 62 HDD. This seemed to be somewhat in line with similar HDD's in the prior heating season. On 1/8/15 I used 363 kWh for 58HDD. This was my highest usage day in the three years that I have lived in this house. The previous high was 220 kWh for a 70 HDD on 1/6/14. On 1/9/15 my usage dropped back to 198 kWh for 54HDD. This still seems high compared the 1/7/15 usage of 147 kWh and 62 HDD, and with similar HDD's in prior years.

My January through December bills totaled 10,009 kWh in 2012, 12,544 in 2013, and 14,908 in 2014. (My billing cycle is about mid-month.) I got a new record (for me) bill of 3223 kWh a week or so ago.

The electric utility's website shows that I used as little as 2 or 3 kWh a day last spring, and a couple of more in the fall days. Our baseline consumption is a bit strange since are often at our rural home during the pleasant spring and fall weather. When we are gone the primary electric usage is the refrigerator and freezer. When we are home the electric lights, electric stove, dishwasher, and clothes dryer add several kWh.

The semi-annual servicing of our system (of dubious value, I now understand) always reported that the system is running correctly. My increasing electric consumption led me to looking further and finding this forum. I understand the concept of a design temperature, but I'm not trying to design a new system. I'm trying to live with the system that was installed when the house was built (and who knows what kind of calculations were made before the system was installed.)

The one major difference between this heating season and last year is snow. Last year there was a foot or so of snow on the ground during the coldest weather. This year there was little, if any. That could have an impact on a 3500 sq. ft. single story home built on a slab (and I have no idea if and how the slab is insulated.)

As a retired auditor, I recognize that trying to fine tune a calculation is really an exercise in turd polishing when key data is either missing or being estimated.

 

So at 10 cents/KWH (I am guessing, I don't know your rate), your annual costs for your entire house including all the other consumers and including heating, cooling and DHW are $1,000 in 2012, $ 1,254 in 2013 and $ 1,408 in 2014 whereas 2014 was about 30% more HDD in my neck of the woods. Overall, that sounds relatively reasonable for a 3500 sqf house single story house in Indiana on a slab.
Yes, your system might be undersized, and you might spend $100 less a year if you would have a 5 ton unit, but is it worth it worrying to much about it now? I think your consumption looks very reasonable for your size house. Although I cannot explain your increase of this year versus last year. Keep your filter clean, and your HP should be happy. Let them measure the performance of the unit at their next dubious service visit.
No, snow should not make any significant difference on your loop performance.

 

Retired don't forgot we had the really low dip the morning of the 8th and there was no sun that day even though it was one of the higher temperature days so the HDD didn't look that bad. See my graph below. Blue is outside temp read on the left axis. Red is my south facing room with large windows. No peak on the 8th for the south room means no sun. You were probably using Aux heat from midnight on that morning of the 8th. Are you on Duke? I think they are more around $0.13 kWh by the time you figure in the fees and taxes even though their bill says $0.10 kWh for the energy.

 

I'm on Indianapolis Power & Light. Their fee structure is a monthly meter charge (two tier depending on usage.) The electric rate is 6.7 cents for the first 500 kWh, 4.4 cents for the next 500 kWh, and 3.18 cents over 1000 kWh if you have electric heat and/or hot water. On top of that, there are a variety of riders that add a little over 3 cents per kWh to all usage, and the state 7% sales tax on everything. I hope that is clear as mud!!

The weather bureau said that 1/8/15 had a low of -7 and a high of 20. However, they say that 1/7/15 had a low of -6 and a high of 12. It seems odd that I used 147 kWh on 1/7/15 and 363 kWh on 1/8/15. The really cold day of 2014 was 1/6/14. The weather bureau said that the low was -15 and the high was 5. I used 220 kWh that day.

To this point, the best information that I can see is that my system ought to be pulling about 20 amps in the second stage. On the really cold days it should be running on second stage about all the time with the 20 kWh auxiliary kicking in when necessary. In very rough numbers the auxiliary must not have run much on 1/7/15. It must have run about eleven hours on 1/8/15. On 1/6/14 it must have run about four hours. Those aux heat run times don't seem quite consistent with the temperatures. You expert folks seem to be telling me that my EWT is probably in the low 30 degree range in the very cold weather. With these temperatures my system would be lucky to put out 1,000,000 btu per day, and my 20kw aux should add about 68,000 btu for every hour that it runs. That suggests that I supplied about 1.25 million btu on 1/6/14 when the low was -15 and the high was 5. It suggest that I supplied about 1.75 million btu on 1/8/15 when the low was -7 and the high was 20. To me, this suggests that something is wrong. Whatever the problem is, it's probably not costing me more than a couple of hundred dollars a year----not enough to justify adding another vertical hole or replacing my heat pump with a larger one. Just playing with the numbers, it almost seems like COP of the heat pump is dropping wildly in very cold weather or that a significant portion of the auxiliary heat isn't getting into the ductwork. Is it possible that the heat pump could draw significantly higher amperage in very low temperatures or that the heat extraction from the loop could drop to nearly zero (because something freezes or???) Is there some way that my 20 KW aux heat coils aren't delivering a significant portion of their heat to the ductwork?

When I bought my house I tried to get as much information as possible about the loop. (I wanted to know where it was located). The only information I could get was the loop installer's memory that he had drilled four 100' vertical holes somewhere in the back yard. I doubt that snow cover would have much effect on the earth temperature at the bottom of the holes, but it might have some effect on the small portion that leads into my house. The snow might have some impact on heat loss through the perimeter of the house foundation and slab, and might affect the heat loss through the roof (the heat pump and all the duct work are in the attic and the attic ventilation isn't the best---especially when the roof vents are covered with snow.)

 

I can tell you're an auditor. How far is your house from the weather station? Are you sure that the two items your comparing (HDD and energy used) are both measured exactly the same (like midnight to midnight)? Sunshine or no? Windspeed? How many times you entered/exited the house? And did you say the geo is on a separate meter?

I think there are too many variables to look at a 24 hour period, as opposed to looking at a 7 day or 30 day period. Give it enough time to average out those rough edges...

 

So it seems that 10 cents/kwh is a good number, on average.

COP is stable and independent of outside temperature, since the source for the heat is stable, with the exception that the unit goes into a higher, less efficient stage.

If the heat element is in the ductwork, it should get in. Yes, higher blower speed might draw more amps, blower at full speed usually accounts for 10% - 12% of consumption.

If loop heat ext ration goes down too far, the heatpump would shut off on lockdown and would have to be reset manually by cutting the power. Although I must say that 4x100 ft sounds very short for a 4 ton borehole, with probably a 5 ton house load on it.

 

Tamar,
There are a number of weather stations in the Indianapolis area. I was quoting figures from the Indianapolis International Airport which seems to be the "official" station for the city. I suppose that it's about 30 miles from where I live. The HDD reported at the airport seem to be very close to those reported at a private weather station about two miles from where I live. I've asked the question about the exact timing of degree days and kWh consumption. I've been told that the figures were midnight to midnight. That sort of information doesn't seem to be "published", and who knows whether the folks who man the phones have any idea when they give out answers. I don't have the sunshine information, but I can say that the subzero temperatures this year were mostly at night. My house seems to get very little solar gain when it's dark outside. I didn't factor in wind speed, and I don't track how frequently I enter or leave the house. Being a retired geezer, I'm not "out and about" much in sub zero weather, although I do fetch the morning newspaper and the afternoon mail. I didn't say that the geo was on a separate meter---it isn't. I have a gas water heater, so I don't believe that my non-geo usage is a major factor in explaining how I used 360 kWh in one day.

docjenser,
I understand what you are saying, but I'm still faced with the fact that it's taking more kWh input to maintain my temperature. At the most basic level, the heating load of my house must have increased or the efficiency of my heating equipment must have decreased.

The 4 x 100' sounds short to me as well. With no written documentation, it may be bad information. Maybe our area has good heat transfer??? I know that the water table is very high in this area.

This morning I started searching for better information on daily temperatures. I found a website that give a great deal more detail than HDD.

http://www.wunderground.com/persona...KININDIA81#history/s20140106/e20140106/mdaily

This website allows interested parties to view weather conditions at about six minute intervals. It rather clearly shows that 1/6/14 (when I used 220 kWh) had subzero temperatures 21.5 hours in the day. 1/8/15 (when I used 363 kWh) started out at -4, warmed up to zero about 10 a.m., and was up to 20 degrees by midnight.

 

Check your air filter, check your heat extraction to ensure your unit is running fine. If those things are OK, then there is nothing on your unit which could explain a 30 % jump.

Don't be too fixated with a single event, only if you should see a statistical trend or significance, you should be worried.

Check into getting us good operational data, like temperatures with needle thermometer. Loop in and loop out for example.

 

Yesterday a neighbor loaned me his infrared non-contact thermometer. (I know that it isn't the recommended tool, but anything is better than nothing.) The insulation around the input and output (and pete's ports) was loose enough that I could get a reading of about 33 degree EWT and 24 degree LWT while the unit was on 2nd stage. I took that as a positive sign.

The unit is in my attic in a "closet" that is about 4' x 8'. The closet is sort of tucked in under the rafters so one side is about 4' tall while the other side is about 8' tall. The supply plenum (or whatever the proper name is) on top of the heat pump is made of duct board. The top of this plenum is jammed against the sloping ceiling on one side. There are round duct "fittings" coming out of all four sides on the plenum. One is an 18" duct supplying one zone. The second is a 14" duct supplying another zone. The third is a 12" duct supplying the third zone, and the fourth is a 10" duct with a barometric damper that dumps into return air plenum. The fitting that comes out directly in front of the closet door is an elbow with flexible duct attached. When you are standing in the open doorway, the duct does an excellent job of blocking the view. For some reason, I stepped back a few feet to pick upsomething. When I turned back around to face the open door, I could see that the top of the plenum was hinged "open" a couple of inches on one side. The foil duct tape that had been holding the top on the duct board plenum had failed along two (or more) edges and the unit was dumping a substantial amount of heated air out the top. As a stopgap repair I pushed the top back down (with the unit off so that I wasn't fighting the blower pressure) and taped the seams as best I could reach with new foil duct tape. I'm sure that my repair was less than perfect because I was working through the open doorway. There is no way that a portly fellow like myself could get into the closet and see/reach all the seams.

This brought up a new set of questions. I think that I will start a new thread to address them.

 

That is probably a big leak right at the supply plentum. Air is going to take the path of least resistance.

 

That could fully explain your increase in electricity, and lack of performance to heat your house. If your loop is at 33 F despite you taking much more heat out, that means it is performing very well.

How is your duct system designed if only one zone calls for heat? Bypass damper?

 

It has a bypass damper dumping into the return air plenum. I can't imagine that the 12" duct to the smallest zone plus the 10" bypass duct are the ideal set-up for stage 2 or three when the blower output is over 1400 cfm.

Now that I've patched the plenum as best I could, I've noticed some changes. It's now down to 17 degrees outside and the system is still running on stage1. With all three zones competing for the output, the air coming out of the registers sure feels cool!

 

Arghh, that is why I had asked.....bypass damper significantly increases the return air temperature, which increases your coil temperature, increases refrigerant pressure, significantly reduces efficiency.

 

I realize that I am "beating a dead horse", but I would like to toss out an observation.

Before I found my problem with the major supply leak in the attic, I played with a borrowed non contact infrared thermometer. I noticed that the vent fans (and I have a load of them with 4 1/2 baths and two fans located in my enclosed porch where someone intended to install a hot tub) showed pretty cold temperatures when I pointed the thermometer at them. The cause didn't register at the time. Now that my attic leak is fixed, the fans actually show a warm temperature.

I now recognize that my leaking supply plenum in the attic was functioning as a "blower door" test on my house and that the vent fans offered the path of least resistance to suck in make-up air. Now that the plenum leak is fixed, the fans are probably being heated by the chimney effect of some hot air leaking out.

I looked at a lot of HVAC forums in the past couple of week. I've seen a lot of posts talking about leaks into unconditioned spaces, but I haven't seen any mention of pointing an infrared thermometer at a bathroom vent fan on a cold day being a way to detect the existence of (but not location of) a supply system leak.