Help with my high energy bills for new efficient home
Chrisroche
| Posted in Energy Efficiency and Durability on
-Edit- Turns out the heat pumps needed fine tuning. The contractor did not tighten line sets enough when installed so the units lost refrigerant. Additionally I had the contractor set the heat pumps to “high insulation mode”, which also helped. Electric in January was down to $150 for heating, water and electricity.
Last year I finished building my new high-performance house and I just made it through my first winter up here in NH. While the home performed phenomenally well on paper when I had it audited for the energy star program, my electrical usage seems to indicate the opposite The HERS rating came out to 33 and the blower door test came out to .46 ACH. The strange thing is, my electrical usage has been ranging from 2,000 kWh in Feb when the average temperature was 20F. In April the average temp was 36F and we used 1000 kWh.
It is just my wife and I living here. We have kept the house as a constant 70F upstairs and 65 in the basement, which has no windows and is a walkout on on the short end.
A little bit about the home.
The house is a ranch with unfinished lower walkout. It is 65 ft by 28 ft and is roughly 1800 sq ft on the first floor and same for the lower. It has 9 ft ceilings.
It was built with a double stud wall, dense packed cellulose. R40 walls and R60 attic. The windows are all triple pane Intus and the whole interior has a Siga membrane that has been air sealed with tape. The basement has spray foam interior walls and 2 inch rigid foam on the exterior and under slab
The house is ventilated by the Panasonic intelli balance 100 and we keep it at a constant 50 CFM running 100% of the time.
A little bit about the home.
The house is a ranch with unfinished lower walkout. It is 65 ft by 28 ft and is roughly 1800 sq ft on the first floor and same for the lower. It has 9 ft ceilings.
It was built with a double stud wall, dense packed cellulose. R40 walls and R60 attic. The windows are all triple pane Intus and the whole interior has a Siga membrane that has been air sealed with tape. The basement has spray foam interior walls and 2 inch rigid foam on the exterior and under slab
The house has all energy star appliances, with a heat pump dryer, 80 gallon rheem heat pump water heater and led lighting throughout the house.
The house is ventilated by the Panasonic intelli balance 100 and we keep it at a constant 50 CFM running 100% of the time.
The house is heated by two separate Fujitsu heat pumps. One at the (open concept area) end of the house is heated by a single head AOU9RLS3H. 9K BTU
The other end of the house and basement are heated by a two head system
AOU24RLXFZH, which has 2 9K heads. One heats entire basement and other heats the master bedroom.
Any thoughts why my electrical usage is so high? Or is this normal? I had a service tech come out and look at the heat pumps and he said both were properly charged. We do not turn lights on any more than a normal family of two would. But with an electric bill of $370 in Feb, this house certainly doesn’t feel like a home that’s supposed to be at least 33% less energy usage than a code built home. Thank you all for your help!
Chris Roche
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Replies
Have you considered just buying a sense monitor or other electric monitor? (there’s a way better, more expensive one) on the market.
That should debug the problem quickly.
Hi Ryan,
I have thought about it, but I have read conflicting reviews on how it performs reading electronics with variable speed motors such as heat pumps, ervs and what not. I was looking at purchasing the Brultech GreenEye, supposedly it has the ability to monitor individual circuits and runs around $500. https://www.brultech.com/greeneye/
I have a 32 channel Brultech that I'm happy with. Seemed like a much better deal than TED.
Another vote for the Brultech GreenEye. I used it with Smart Energy Groups for years. When SEG started charging, I bought the Brultech Dashbox for monitoring. Otherwise, the SEG subscription would cost more than my electric bill! (7.5 kW solar array, heat pump water heater, heat pump dryer, electric baseboard heat) The Dashbox has a built-in web server which you can share on the internet or keep private.
Chris
My guess is the issue is your multi split.
I have a 24kbtu LG multi split and the lowest power I've seen on it is 750w (540 kWh per month) no matter the number of heads on or set point.
In your case im pretty sure the multi is oversized for the loads and not running in an efficient range.
A simple test would be to turn it off and monitor your power meter and see if your daily energy use improves.
Probably a space heater to heat your bedroom would use less energy than the multi split.
That's what I am wondering, I guess I am also curious to see what other people are getting for energy usage for other similar homes. For an energy load like I am seeing now, I would need a 20k solar system, that just seems crazy.
What is your power usage like in the months when you need little heating or cooling?
All we can do is guess until you measure where the electricity is going.
Do you out door unit cycle off and on when it is below 30° or do they run constantly?
How do you heat your water?
Do you have a well with a pump?
A lot of electronics sold today do not really turn “off” when you push the power button, the lights go out but the power usages change very little.
Consider buying a monitor like TED 5000 with spider this would allow you to monitor 8 circuits plus the mains.
http://laaudiofile.com/ted_pro_home.html
Walta
Chris,
My experience in monitoring superinsulated homes and yours easily meets the qualification goes like this. In the 5 homes I followed they ranged from .9 t0 1.5 Btu per square foot per heating degree day depending on size and solar access.
Your home of 3,600 sf total for an estimated 1,500 Hdd for February should use between 1,424 kWh and 2,373 kWh if you were heating with electric baseboard. I would think your home being very airtight would trend towards the 1,424 kWh. I have to question the operation and efficiency of the heat pump. With the summer months coming on it will be easy to determine your non heating electrical usage.
I am using right around 9 kWh per day for the month of April (265 kWh) heating with natural gas.
Chris,
Your electric usage seems quite familiar to me, as does your questioning where it all goes. The seemingly phantom consumption of KW may relate to your mini-split set up or the water heater may be behind some of it. It takes a lot of wall warts to consume enough to tweak the bill. Your description makes it sound like your home is all electric, so I am assuming that you don't have a big range hood throwing your heat outside. On to what I have found from experience four years in to my own energy mysteries.
My wife and I are now finishing our fourth winter in our very similarly efficient home. Whole wall of R-36, ceiling/roof of R-52, complete Henry Blueskin wrap for air tightness (design is outsulation with dry to inside moisture handling). Our living sf is about 2500 over three levels and the basement is also insulated to R-15 on the outside and under slab. Total conditioned space, about 3400 sf. The basement free runs at 58 during winter. I use space heaters when I need to putz around in the shop.
Heating degree days are wildly variable here at 8,000 ft in CZ6. We have had snow the last two days and lows below freezing over night. Other years I have worn shorts in April. I am assuming you aren't on top of Mount Washington for weather purposes, so I think we are likely well matched for weather. I originated from back east and my memory of it is mostly the general conditions of being wetter there.
We used 21,000 plus KWH 2016, 17,828 KWH in 2017 and 19,580 in 2018. The first year was extra distorted due to painting and what not requiring lots of ventilation and heat loss. Average HDD here with a base of 65 is about 7100 with micro-climate variations making that a guess rather than a hard guideline. I will leave it to the data driven types on GBA to advise you on the effects of using 70 as your house temp. I seem to be falling in the 1.2 BTU/sq ft/1 HDD range for heat, which is pretty good for all resistance heat.
And please everyone, spare me all the analysis of why I should have mini-splits, I know. The local conditions of vendors and repairs did not support the obvious choice. Besides, my wife and I differ on what temperature each room should be, which also explains my less than firm grasp on how to calculate our per sf heat use. Happy thermostats make a happy life.
Anyway, our baseline usage seems to clock in at a hair under 1KWH per hour no matter what we do. We have 90% LED lighting by fixture count and probably similar consumption ratio for lighting. Induction cooktop, electric ovens, one fridge, one freezer, dishwasher, two computers, two TVs, top load washer and electric dryer. All very normal and typical for two people . Also have an 80 gallon Marathon electric water heater which may be the energy pig in the system.
Entry temperature of the water supply (not on well) here can be as low as 45 and seldom higher than 52 so the delta T ranges from 80 to 73 with a set point on the heater of 125. If you calculate the BTU input needed to raise a gallon of water 80 degrees you should get 666 BTU's (devil is in the details as always). Worst case of 80 gallons used per day would require 53,312 BTU's or 15.6KWH of energy. This would be more than half of our daily minimum of 23KWH in July. It is still a third of our usage total if one assumes 40 gallons of actual hot water consumption and zero losses on the tank. I won't point any fingers as to why that amount would be even remotely possible on a daily basis as happy shower heads also make for happy life for me. I will leave it to your household to "discuss" who takes too long showers. Do you by chance have a deep tub user in the household?
All that said, you may actually be doing just fine for energy usage. New houses do take some time to stabilize the mass thermally as the moisture levels are leveled out. Depending on how you have chosen to insulate the basement level, the losses there may be a bit more than calculated. Even as thoroughly insulated as mine is, I am finding the huge heat sink of concrete very slow to cooperate with keeping the temp over 64. It was more than a year before I felt the overall house had settled into its new life.
I have to observe that two 9K head units being fed by what I think is a 24K unit might be somewhat of an issue due to potential short cycling. A 9K unit in a bedroom seems very high. Our 17 x 14 master with a design point of -10F and two large windows and a door called for under 4K if I remember correctly. I do not have a good grasp of mini-splits so I best defer to others on this point.
My own analysis of going solar put the required size at around 15KW of panel area for our sun rating, which is probably higher than yours. This did not include any amount for future electric car loads. Seems like I would need to consider that factor more now. We are fortunate to have a local power company that is still amenable to KW for KW trade, so our summer production would offset our winter usage nicely. One thing to watch for is whether parity of KW is obtainable and also size limits. Our local service does require special review for permitting installations in excess of 10KW. If your power company is at risk of being bought up, consider the risk of being orphaned for power exchange rates or even totally being denied compensation.
Hope this long ramble through the thickets helps in your quest to find the secret gobblers in your home.
What is your relative humidity in the winter? I wonder if you're over-ventilating.
I was wondering this too, but we have been averaging 45-55 humidity.
Chris: my house in Maine has about 1650 square feet of conditioned space, on an insulated slab. Similar windows, insulation details and air tightness. We use about 10,000 kwh per year. Only significant differences from your house are an electric resistance water heater and a hot tub in an insulated, unconditional space. We get about 8,000 kwh from our pv system.
Your house is twice the size of our house. I don't think your power use is too out of the ordinary. But as mentioned above, the multisplit may be a cause.
I'm curious as to why there are only 2 zones on the AOU24RLXFZH? I suspect a chunk of it is not having sufficient load for the multi-split to operate efficiently.
Overall efficiency would likely rise if the ASU9RLS3 on the open space zone was the third zone the multi-split rather than a separate AOU9RLS3H compressor. (It's likely that the basement zone would be covered by an ASU7RLS, but that's why you do the Manual-J before specifying the equipment.) That would give the AOU24RLXFZH more load to work with. It's legit to hang heads totaling 130% of the output of the multi-split on that series, so 3 x 9K= 27K of head on a 24K compressor isn't pushing the limits by any means. Even installing an ASU12 in that open space zone would still be fine with the other two ASU9RLS zones if that would make it closer to the same capacity/load ratio of the other two zones. (30K / 24K= 125%, which is still less than 130%.)
Without more analysis I can't say for sure if that's THE primary efficiency issue, but it's a likely contributor.
If you already have the Manual J, what are the design loads of the basement zone, the open space zone, & other end of the house zone, separately, and at what outside design temperature?
I would buy a efergy energy monitor for $150 and monitor the mini splits electrical consumption. Seeing the live electrical consumption has been amazing in seeing how these units run and setting them at there most efficient operation.
2000 Kwh for Feb. That makes me feel good. I looked at my meter the other day and it read just over 1800 Kwh on a new meter that was installed last Feb. 2018 The only way to lower your electric bill is to use less. Is your laundry running every day instead of buying an extra pack of socks, dryer instead of clothesline, how many showers a day instead of a sponge bath, dishwasher instead of hand wash, tv on as opposed to off, computer on instead of socializing, using stove as opposed to outdoor grill, using an electric mixer instead of a spoon, raising thermostat instead of using a blanket, lights on in rooms your not in, electric toothbrush or manual, hair dryer or towel ......??????
> What is your relative humidity in the winter?
> here in NH ... we have been averaging 45-55 humidity.
This normally leads to a high risk of wall/ceiling moisture problems.
+1 on getting more detailed power usage readings.
That depends on the climate. I can't consistently get my humidity below 45% summer or winter here in the PNW. Right now we have no heat on, the windows open, and it is 51%.
That's right. Wintertime outdoor dew points in the PNW aren't very different from summertime dewpoints. In New Hampshire wintertime dew points are MUCH lower than in the PNW, and in summertime quite a bit higher. With adequate ventilation (even below ASHRAE 62.2 rates) it should be possible to keep wintertime indoor RH under 40% without much trouble.
Chris, here's another data point for you. My home is similar to yours and I get slightly less energy use for slightly warmer temperatures.
My weather. December, January and February avg. temperatures this year were each ~25°F. The design temp. is -6°F and annual avg. temp. is 40°F. Call it a warm zone 7. Unlike you, I’m at 9,400’.
Here’s a summary of the house so you can compare the two.
The house is all electric with a ranch style main floor and a smaller footprint walk-out basement: The conditioned area is 1,960 sq. ft. main floor and 832 sq. ft. in the basement. There’s an additional 482 sq. ft. inside the thermal envelope that’s unconditioned basement.
Conditioned areas are set at 70°F, unconditioned basement floats at ~ 63°F.
Heating: Two Fujitsu minisplits: one on the main floor and one in the basement. Each one is a15RLFFH floor-mounted cold climate unit. That’s the AGU15RLF indoor unit and the AOU15RLFFH outdoor unit. They put out about 6,560W each at -5°F (11,100 btu/h, corrected for altitude). The open staircase between floors allows the basement unit to help out the main floor in winter.
More heating: an additional 3,000W of electric heating, primarily in the corner rooms of the house. These are set to 66°F in winter and will be 60°F spring through fall. We like cooler bedroom temperatures and leaving the bedroom doors open gets the bedrooms to 68° to 72°F over the course of the day in winter. The bedroom cove heaters don’t even come on unless the outside temperature drops below about 10°F.
Appliances: Rheem 50 gal. HPWH and drainwater heat recovery, electric clothes dryer, induction stove. Energy Star all around.
Insulation: double stud walls R36 on three sides of the main floor (that’s corrected for thermal bridging) and R45 (also corrected) on the north wall and all non-foundation basement walls. Foundation walls have R10 above ground and that extends below ground 2’. Foundation walls also have R10 foam full height plus R10 stud wall on the inside. Slab has R20 underneath. The attic is 22” of cellulose, call it R75. Windows are Alpen 625, all R5 and higher.
Air flow. The home has an ACH50 of about 1.5 (I need to run the final test) and a Panasonic intellibalance ERV running at 60 cfm.
Energy Use: the total monthly electricity usage was 1,700 kWh, 1,475 kWh, and 1,500 kWh for December through February. The average temperature for each month was the same at 25°F. Why the variation between months? I put it down to variability in the wind (quite a lot of that at times) and the amount of sun. By the way, the house unoccupied with the heat off and the water heater set at 135°F (not vacation mode) consumes on average about 360 W.
If I extrapolate from my 25°F avg. temp. to your 20°F value, that adds an extra 180 kWh (ish) per month.
Your measured 2,000 kWh for February seems reasonable.
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