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  1. #1
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    Bosch replaced 34yr old heat pump - same power usage

    I need some help tracking down my power usage issue. I have a brand new Bosh IDS 2.0 5 ton condenser with 4 ton Bosh 2.0 air handler. I've had it in about 2 weeks are started comparing my daily power usage compared to similar temperature days with the 34yr old Goodman heat pump. They are virtually identical. I hear people talking about new ones being substantially better than even 10-15 yr old units.

    I'm not an HVAC guy, but I can do electrical. So this past weekend I installed a home monitoring system and got it up and running and have real numbers to throw at it instead of just total usage the way I did a week ago. Please look at all this and let me know if it is abnormal. This is all data from this morning. We had an overnight low of 30 degrees here. As you'll see in the graphs, I let me heat get down to 60 overnight and bring it up in steps to 64 then 67 then 69 about every 2 hours in the mornings.

    Here are my observations that cause my questions. Based on the power graphs, it appears that my heat strips are occasionally running when my thermostat is not calling for it. The first picture is from my home automation system. The green line is the temp set point on the thermostat. What sticks out to me is that a couple times between 6 and 8am, the temp drops in the house even with the system running. Why would my temp be dropipng even while the system is actively in heat? The brown area in the first picture is when the thermostat is telling my home automation that the system is calling for heat.

    The 2nd photo is my energy monitoring system that I just put in this past weekend showing what the current transformers are reporting for the air handler and compressor (and the total) during that period. It is showing severe spikes that appear to be emergency heat that my thermostat (last picture) is not showing. It has the dark red showing about 8 minutes of strip heat sometime between 7AM and 8AM but no other occurances.

    As for the data that made me question all this to begin with I went back and pulled daily power usage from my power companies web site and used it along with historical outside temp data and compared a whole years worth of hot days, cold days and days where the system would not have run much at all... and so far in these 2 weeks, the heat only portion seems to be very close to what we were using with the 34 year old system.

    Additional info that makes me think something is fishy... Previous year total day averages.

    Past year total power usage average per day = 80 kwh
    Past year total power usage on days where the high was less than 70 AND the low was greater than 58, total power usage those days average is 65 kwh
    Hot day average was 86.04 kwh
    Cold day average was 87.19 kwg
    Peak on super hot or cold days is 125 - 130 kwh

    So far this new Bosch does not seem to be doing much better.
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  2. #2
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    BOSCH IDS 2.0 BOVA PRODUCT INFORMATON

    ~ 4 KW per Table 9 … Seems to correlate
    ______________ with your power tracking for the 5 Ton system.

    https://www.bosch-thermotechnology.u...04.2019_us.pdf

    ___________

    ~ 8 minute Power Spike: I believe it maybe the DEFROST Cycle.
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    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  3. #3
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    Thread Starter
    Thanks for the reply on that. What would likely be causing the excessive run time and the temperature drops while the system is running? If you notice the dips on the first graph approximately 1 per hour... I believe that is because I have the thermostat option turned on that runs the fan only once per hour for 9 minutes. I think it is just the air getting stirred up in the house. But those same dips even seem to be occurring even when the heat is actively being called for which seems really strange.

    Would it be normal for this thing to run from 5:52AM to 10:22AM to bring my temperature up from 64 to 69 with the outdoor temp being 31 to 43 during that time period for a 2100 sq ft house? A little over a degree per hour?

  4. #4
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    Thread Starter
    Ok.. In anticipation of you or someone else saying that this is normal if the heat strips don't run, I did some more interesting math and I think I need to re-think the setpoint for allowing the heat strips to kick on. Right now, I have my heat strips forced off unless the is greater than a 4 degree differential between the thermostat and the actual temp. I also purposely am bringing the temp in the house up in less than 4 degree increments every 2 hours.

    The end result is that I am sing 30 kwh of electricity for 4 degrees of temp rise in the house (when it is approximately 38 degrees outside, and taking into account the extra power usage during those defrost cycles, I'm showing approximately 6kwh used per hour of run time) when I have my settings tweaked to avoid heat strip usage as much as possible. Based on what I have seen so far I could probably do that same temp rise with 20kwh of power when using the strips. I can't calculate yet what the tipping point is between run time where adjusting temps with HP only versus HP plus strips becomes cost effective, but I think the above is well over that point.

    I'll try tomorrow.

  5. #5
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    Thread Starter
    Here is a graph showing my total 60 - 69 inside temp rise with approximately 38 degree outside temp and I had the system tuned to avoid running strips. They only ran for a very short period of about 8 minutes outside of the defrost cycles. It is overlayed with cumulative power usage for that period. I'll compare to tomorrow where I'll set the thermostat to more readily use heat strips and bring the temp up quicker over a much shorter period of time.
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  6. #6
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    NORMAL TEMP = 69'F
    ______ SET BACK SHOULD BE LIMITED TO 65'F

    YOUR LOCAL Temperature BIN DATA should be used to determine actual Energy Use
    given your BUILDING THERMAL ENVELOPE and BOSCH 5-Ton HEAT PUMP

    The electricity seems to be used more for OTHER USES than the HVAC loads.

    ----------
    Additional info that makes me think something is fishy... Previous year total day averages.

    Past year total power usage average per day = 80 kwh

    Past year total power usage on days
    where the high was less than 70
    AND the low was greater than 58,
    Total power usage those days average is 65 kwh
    { Adjusted to 53 IN Example below }


    Hot day average was 86.04 kwh
    Cold day average was 87.19 kwg

    Peak on super hot or cold days is 125 - 130 kwh
    _________
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    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  7. #7
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    All those numbers make me dizzy. But...

    What thermostat are you using?

    I had a customer who absolutely had to install a Nest. He set a balance point in the stat. That was using more electric than before. Turned off balance point in the stat and all was good.

    Down to 5 degrees, there is no reason for the Bosch to run electric heat except during defrost. Unless there is something that is not set up properly or an error on the install.

    Me thinks you are overthinking this problem.
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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  8. #8
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    Your tstat doesnt control the electric heaters during defrost, they are turned on via the defrost board. Heatpumps do not like large setbacks, so if your weather is going to be similar to what you've been having then try for a week doing a max 3* setback and see what happens. I'm betting your going thru a defrost several times a morning doing that, also the colder you keep the inside the lower the discharge gas temp, so your not just going into multiple defroster but your also losing capacity

  9. #9
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    Might want the installing contractor to recheck the charge.
    Contractor locator map

    How-to-apply-for-Professional

    How many times must one fix something before it is fixed?

  10. #10
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    @ dan sw fl

    The detailed usage data came from an iotawatt energy meter that I installed this past weekend. I'm getting the data from a current transformer on the outside unit circuit and the inside unit circuit and combining them.

    The overall usage data is straight from my power company daily usage historical data. As of this past weekend I now have the data from my iotawatt. The first two days match up within 1/2 kwh between my iotawatt and the power company report. It looks like they round to the nearest whole unit, so it may not even be 1/2 kwh off. For example the 11/25/19, my iotawatt shows 63.5 kwh total and 33.8 of that attributed to the condenser and airhandler circuits in the panel. My power company shows 64 kwh.

    @joemach

    My thermostat is a radiothermostat CT80. For 11/25 I had the aux heat set to kick in at 4 degrees or more off of requested indoor temp. When this model of thermostat is set in 3h2c mode (which it is), it will start heating with 1st stage only as long as temp differential is less than 4 degrees. If 1st stage does not reach set temp within 15 minutes 2nd stage will come on. Aux heat will not come on at all unless temp is more than my controlled setpoint, again which yesterday was set to 4 degrees. Yesterday I also had the system tuned to bring the temp up in 3 degree increments every 2 hours to further keep from running the heat strips.

    Today I have the setpoint set to 3 degree differential and brought the temp up much more rapidly to ENCOURAGE the strips to run. Charts for this morning are below. It did reduce my overall kwh with similar outdoor temps today as yesterday. So basically nearly the same indoor temp rise, nearly the same outdoor temps between yesterdays charts and todays charts. The only difference is yesterday I had the system tuned to avoid strips. Today tuned to encourage it. Today used LESS energy. Yestersay there was just shy of 30kwh used by just the bosch equipment during that temp rise from 60 - 69. Today the system used 22.8 kwh for the same rise in temp. So I think the system may not be performing up to standard.

    @makeitcold

    What do you mean losing capacity. Does todays new information add anything new? I'm still concerned about the dips in temp and the super slow heat rise after the strips turn off even today. My home is 2100sqft but my living room is 25ft x 25ft in a huge A-frame with 25ft up to the peak. Is this simply the way it is going to be? The old system took a while also, but we always thought it was just because it was old and inefficient. In todays data, those dips, at least after 7:40 were not due to doors being opened as people left either. The last person was out at 7:40AM. This new system is moving MUCH more air volume and the returns are much better placed. The house is definitely much more evenly heated than before.

    Just in case anyone asks what the rise and fall in my set temp is right about 5AM, its my cooling program versus my heating program. We went to bed last night and I kicked the system over to the cooling program to get the temp down below 67 so we could sleep. Then just left it on cool all night long and the indoor temp fell to 62.5 degrees on its own. The cooling program is set to let the temp rise to 72 as shown. I kicked it over to the heating program which is set to heat only if the temp gets down to 60 degrees overnight (we like it cold at night) and then it 5:20 it starts bringing the house temp up.
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  11. #11
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    Heat pumps lose capacity as it gets colder outside, they also will lose capacity if the building is cold. Not to say it's not capable of pulling back up, but HP's are much happier maintaining temp rather than overcoming it. Having the strips locked out as you do causes longer run times of the condenser, requiring defrost more often. I'm spitballing here as I have no idea if the refrigerant charge, airflow and system setup are correct. I'd be curious as to what your temp rise is when it starts the morning warm up cycle with the strips turned off at the breaker.

  12. #12
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    How many stages of backup heat do you have in the air handler?

    I know that Bosch system wants you to use a simple thermostat as possible. 2 stages of heat. Stage 1 is heat pump on W2. Stage 2 is back up heat. If you have stage 3 that would be W3.

    You need to let the system do the thinking.

    From the spikes on your chart, looks like back up heat is coming on full force. This could be dues to the thermostat.

    By best recommendation is to just set it and forget it. Set it at the temperature you like and change it in the Spring. You should call your installer back and make sure you system is properly set up for your temperature zone. I will bet that it is not.

    You don't have 2 stages of cooling. The system handles that. Let it do its job.
    Can someone please explain to me -
    Why is there never enough time to do it right the first time, but plenty of time to do it twice?


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  13. #13
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    ENERGY ESTIMATE

    __ 1985 Built // 2,100 Sq Feet // Piedmont NC

    _ REF.: ASHRAE FUNDAMENTALS, CHAPTER 14,
    _____________CLIMATIC CONDITIONS, 2017
    _ HDD 3,533
    _ CDD 1,454


    A NORMAL Heating & Cooling EQUIPMENT SELECTION AND OPERATION
    may use ~ 12,550 KW-HR per year.

    ___ ENERGY USE BASIS: MY CALC INPUT FORM 2100 SF ... 27NOV19
    ___________________ ________ ____________________ _______

    SPECIFIC INPUT: Lines 5, 8, 11, 12, 13, 15 through 26, 30, 31, 39 & 42
    _____ PRESUME
    R-11 WALLS
    R-26 CEILING
    R-13 FLOOR

    WINDOWS: 323 SQ FT GLASS
    _________ U-Factor 0.49, S.H.G.C. 0.60
    ____ _______________ __ _____ ___________
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    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

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