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  1. #1
    Join Date
    Jan 2013
    Location
    sterling heights Michigan
    Posts
    26

    I need help choosing electric service and heat pump set points with my new Lennox 21

    I am not sure of the electric service interruptible or time of day for space conditioning that I need to use for the separate meter. I also need to know what outdoor temp to lockout the heat pump and furnace. I want to save the most money on my utility bills. I live in Sterling Heights Michigan. I use DTE FOR ELECTRIC and consumers energy for natural gas. I would love some help with this. 110000 BTU and 4 ton with a 5 ton indoor coil. 2453 square feet built with 2nd floor in 79 with sealed duct in basement. I also added r30 to ceilings for a total of r45. 2nd floor walls had r4 added for a total of r19 . 1st floor walls have a r 15.New = all Lennox new 98 furnace XP21, heat-pump,indoor cased coil pure air, power humidifier, I-comfort Wi-fi stat. It cost a bunch, now I have to choose electric service and set points.When it was charged they didn't use a weighed calculated charge they just used super heat or gages , they added 19 ounces and the instructions wanted 33 ounces then checked with super cool. Should I be concerned about efficiency with the 14 ounce discrepancy?
    Last edited by Warlockamized2; 01-13-2013 at 08:47 PM.

  2. #2
    Join Date
    Jan 2013
    Location
    Central, FL
    Posts
    29
    If they used the Lennox sub cooling chart to charge your system you should be fine. The correct charge can vary with line st length. Enjoy you new system.

  3. #3
    Join Date
    Jan 2013
    Location
    sterling heights Michigan
    Posts
    26
    I calculated in the extra line set also. 3 ounces per 5' for beyond 15'.

  4. #4
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,098
    How do you know they added 19 ounces if they didn't have scales?

  5. #5
    Join Date
    Jan 2013
    Location
    sterling heights Michigan
    Posts
    26
    They had a scale. She ( one of the installers) told me that 19 ounces were added. The heat-pump came per charged with 13 pounds. The use of that coil called for an additional 1 pound 5 ounces and the line-set needed another 11.4 ounces, for the weighed initial charge . I took the cooling class in trade school 26 years ago. I am a sheet metal journeyman. I also had a semester class in collage for energy auditing 29 years ago.

  6. #6
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,296

    Overview of Selecting and Operating new Dual Fuel Heating Equipment

    Quote Originally Posted by Warlockamized2 View Post
    I am not sure of the electric service interruptible or time of day for space conditioning that I need to use for the separate meter.

    I also need to know what outdoor temp to lockout the heat pump and furnace.

    I want to save the most money on my utility bills.
    I live in Sterling Heights Michigan.
    I use DTE FOR ELECTRIC and Consumers Energy for natural gas. I would love some help with this.
    110,000 BTU and 4 ton with a 5 ton indoor coil.

    2,453 square feet built with 2nd floor in 1979 with sealed duct in basement.
    I also added r30 to ceilings for a total of r45. 2nd floor walls had r4 added for a total of r19.
    1st floor walls have a r 15.

    New = all Lennox new 98 furnace XP21, heat-pump, indoor cased coil pure air, power humidifier, I-comfort Wi-fi stat.

    It cost a bunch, now I have to choose electric service and set points.
    Set points are already established if you are currently living in this 2,453 Sq.Ft. two-floor residence.

    I believe Time-of-Day rate could easily at least Double or triple your electric bill.
    If you wish to select interruptible electric service on the heat pump,
    the heating controls must be set-up for auto switch-over to gas furnace or be prepared to have the house cool at least ~2'F per hour.

    IF all that equipment was just replaced, WHERE Is the Load Calculation?
    You mention ceiling and wall r-values, however,
    the Windows and Infiltration are BY_FAR the MAJOR contributors to Heat Loss.

    Actual Area of windows (maybe 320 square feet total ? ) and U-Value ( ~0.5?_, double pane, argon filled?)
    along with actual infiltration (? 0.5 Air Change per Hour -A.C.H.).
    ARE generally Good STARTING POINTs to determine total Heat Loss ( gain) prior to signing contract for heating ( cooling) equipment replacement.

    How did the mechanical contractor determine 110,000 BTU was Actually necessary?
    WRONG response here is, that's what the original equipment was.

    Is the heat pump set to run now as low as 34'F, _ _'F or 42'F?

    Selecting heat pump lock-out set point is dependent on the Heat Loss balance point.
    One might make a _wild guess_ that the overall building heat loss would be ~72,000 BTU/hr at ~-2'F design temperature.
    .:. Heat loss at 35'F would be in the ball_park of 35,000 BTU/hr.
    _ IF _ those guessed values are close, then the heat loss balance point would be estimated as ~36'F for a 4-ton high H.S.P.F heat pump.

    Economic balance point _ Later.
    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
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,296
    Economic balance point = ~ 50'F.
    Minimum switch-over set-point to Natural Gas = ~ 50'F
    Heat pump may provide about 10% of the annual heating energy

    ~ $0.82/ therm Natural Gas
    http://www.consumersenergy.com/content.aspx?id=1254

    ~ $0.13 /kwHr
    http://www.dteenergy.com/residential...alculator.html

    $0.13 ….. $ / kw DTE
    100,000 ….. BTU per hr / Therm
    3,413 ….. BTU per hr / kW
    29.2997 ….. kW/ Therm
    $3.81 ….. $ /Therm
    ... 4.6 ….. C.O.P. needed to equate energy costs
    $0.828 ….. Equivalent $/Therm at given C.O.P.
    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

  8. #8
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Are you using time of day off peak rates for the calculations? dual fuel cna be ideal for time of use. Usually the off peak is almost 1/2 the regular rates. The trick is preventing the heat pump from running during peak periods. Some communicating thermostats have inputs ot lock-out the compressor during peak periods. I think it's also possible to use a programmable thermostat to interrupt at least 2nd stage durign peak periods and intentionally use daytime setbacks to force the system onto the aux gas heat.

    You equipment is very generaously sized, so setbakcs should work pretty well.

    Don't forget to add about 100-400W atts or I think around $0.03-0.08 100k BTU on the gas furance for it's electrical consumption for the blower and ID fan. I think that gets missed a lot. Blower power is already factored into the heat pump calcs.


    On off peak, and depending on whether you have stepped rates, you should be closer to $0.05-0.08 off peak. But it will go up on peak. Where I am we have 3 steps, 0-500kwhr, 500-1200kwhr and 1200+. The rates drop siginificantly at each step. Natrual gas does drop a little with higher volume use and you spread out the fixed fees, but not as much.

  9. #9
    Join Date
    Jan 2013
    Location
    sterling heights Michigan
    Posts
    26
    Interruptible costs between June and October are 11.368 cents per kilowatt hour and November through May is 9.175 cents per kilowatt hour. Time of day rates are 13.48 cents per kilowatt hour June through September 10 AM to 7 PM then 6.162 cents per kilowatt hour June through September for off-peak hours, Then October through May on peak hours 10 AM to 7 PM is 7.271 Cents Per kilowatt hour and the off-peak for October through May 6 .258 cents per kilowatt hour. I can use the program and dial down from 7 AM to 4:30 PM weekdays September 7 to June 12. All windows are argon filled double pane. I have a wood burning fireplace and leave the flu closed but it is still sometimes drafty. I have an insulated and sealed banjoist. I have the furnace locked Above 50F and the heatpump locked out below 35F

  10. #10
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,296
    Quote Originally Posted by dan sw fl View Post
    Economic balance point = ~ 50'F.
    Minimum switch-over set-point to Natural Gas = ~ 50'F
    Heat pump may provide about 10% of the annual heating energy

    ~ $0.82/ therm Natural Gas
    http://www.consumersenergy.com/content.aspx?id=1254

    ~ $0.13 /kwHr
    http://www.dteenergy.com/residential...alculator.html

    $0.13 .. $ / kw DTE
    100,000 .. BTU per hr / Therm
    3,413 .. BTU per hr / kW
    29.2997 .. kW/ Therm
    $3.81 .. $ /Therm
    ... 4.6 .. C.O.P. needed to equate energy costs
    $0.828 .. Equivalent $/Therm at given C.O.P.
    FORGET THE ABOVE /i\

    OCTOBER THRU MAY
    . . . . . . .MAX TIME_OF_DAY: $ 0.073 / KW-HR
    $0.073 ... $/kW
    100,000 ... BTU/ Therm
    3,413 ... BTU per Hr/kW
    29.2997 ... kW/ Therm
    $2.139 ... $/ Therm
    _ 2.62 ... C.O.P. ________________
    $0.816 ... Equivalent $/Therm

    Heat pump is cheaper to run > ~20'F ( not accounting for defrost cycle)
    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

  11. #11
    Join Date
    Jan 2013
    Location
    sterling heights Michigan
    Posts
    26
    My current Standard residential Electric rate is 11 .915 cents, hour for the first 17 kWh Per day, for additional kilowatt hours per day it's 13.6 cents per kilowatt. I need to know what is cheaper, time of day or Interruptible, figured yearly. Because once I have the second meter installed I have to keep it for 12 months. Then I have to know setpoints for that rate. I am thinking of having a energy auditor help me with this or does someone know.

  12. #12
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    6,296

    Cost comparison$ by energy auditor worthwhile

    Quote Originally Posted by Warlockamized2 View Post
    My current Standard residential Electric rate is 11 .915 cents, hour for the first 17 kWh Per day, for additional kilowatt hours per day it's 13.6 cents per kilowatt. I need to know what is cheaper, time of day or Interruptible, figured yearly. Because once I have the second meter installed I have to keep it for 12 months. Then I have to know setpoints for that rate. I am thinking of having a energy auditor help me with this or does someone know.
    I'd say time-of-day October-May due to most of your energy use would be with winter and heat pump use given you're in Sterling Heights.

    DTE Energy time-of day is not what I anticipated. Much lower rates without any penalty over regular rate.

    I can't be sure about specific cases given the various conditions and cost comparisons without doing significant amount of
    calcs on sizing, annual heat load and type of equipment/ heat pump vs furnace load share.
    However, I'd trust my gut on time-of-day rate being cheaper.

    ...
    Dan, formerly of Ann Arbor.
    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

  13. #13
    Join Date
    Jan 2013
    Location
    sterling heights Michigan
    Posts
    26

    Question I now have to pick low set point for heatpump.

    I have ordered an electric meter with schedule D1.7 rate, time of day for space conditioning and water heating. I wont be using it for water heating. Only the heat pump will be using it. Should I cut the heat-pump off at or near the outside temp that it has to have help from the furnace ?

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