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  1. #14
    Join Date
    Jul 2005
    Location
    Orange County, NY
    Posts
    936
    I will have to say " E "......The more screwed the customer gets

  2. #15
    Join Date
    Aug 2001
    Location
    forney texas
    Posts
    17,890
    maybe stupid but I would say A. if you can get heat from the air versus resistance heat it would be more efficient to operate a HP, thats what they are designed for. and the main reason to consider buying one.

  3. #16
    Join Date
    Aug 2004
    Location
    Tyler TX
    Posts
    676
    Balance point does not change. Here is an article that explains it pretty well.

    http://energyoutlet.com/res/heatpump/balancepoint.html
    HVAC Contractor, Tyler Texas.

  4. #17
    Join Date
    Aug 2001
    Location
    forney texas
    Posts
    17,890
    The key word is efficient, if the compressor can heat the home with its amp draw its more efficient then resistance heat.

  5. #18
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,350
    Originally posted by jacob perkins
    Originally posted by shophound
    Thinking out loud here...if I remember correctly, the closer together the suction and discharge pressures are on a compressor, the lower number there will be on the compression ratio.

    So, with a heat pump in heat mode, say it's running a suction pressure around 50 psia, and head is up around 270 psia, that's 5.4:1 compression ratio, whereas if same heat pump was in cooling mode on a hot day running same head pressure psia but suction around 84 psia, that's 3.2:1 comp ratio.

    I will also pick "C" as being correct.
    I think you might have the correct answer,S'hound,but "your thinking out loud" shows you drifted off to the cooling mode...read the question again please.
    I believe I did acknowledge the question as pertaining to the heat mode as noted in your quote of my quote above. I mentioned the cooling mode to serve as a comparison/contrast to heat pump operation in heat mode. In my early days of learning heat pump operation, heat mode operation often threw me for a loop because the parameters were somewhat different from cooling mode. So, in my "thinking out loud" process I tend to reference one against the other to maintain an understanding of both the similarities and differences.

    Specifically, I worded my answer as such because one can actually derive why the compression ratio for a heat pump in heating mode is higher than the same machine in cooling mode. So if you are used to seeing comp ratio's in the 3's during cooling season, it won't throw you for a loop to see comp ratio's over 5 in the heating season, based on the info that the further apart suction and discharge pressures are, the greater the comp ratio.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  6. #19
    Join Date
    Nov 2004
    Posts
    2,927
    Originally posted by shophound


    Specifically, I worded my answer as such because one can actually derive why the compression ratio for a heat pump in heating mode is higher than the same machine in cooling mode.
    Because suction pressure is much lower with a somewhat steady range of condensing pressures (in the heat mode)....

    I am a one single-moded thinker.I cant help it.Heating and cooling in the same paragraph confuses me.


  7. #20
    Join Date
    Jul 2004
    Location
    Southern Alabama
    Posts
    448
    Correct answer is "C"

    "A" is wrong due to less heat being available to draw from, therefore Coefficient of Performance (COP) goes down. COP measures how efficient the heat pump is in the heating mode. BTW COP>1 when you use a heat pump for heating and the compressor is pumping. So, a heat pump will ALWAYS be more efficient than straight electrical heating due to there will always be some heat to remove from the outside air.

    "B" is a cooling rating not heating like COP is, so SEER is the wrong rating here.

    "C" is correct due to the suction pressure being so low. The heat pump is doing refrigeration duty when it gets very cold out.

    "D" is wrong because the balance point is defined as the point where the heat pump supplies exactly the same amount of heat as the structure looses. There is only one point for this. The balance point is used to determine the amount of supplimentary heating required AND, if used properly, when to energize it for maximum heat pump efficiency.

    [Edited by on call on 08-08-2005 at 12:06 PM]

  8. #21
    Join Date
    Jul 2005
    Posts
    19

    Blance Point

    Since the balance point is the temperature outside at which the unit cannot maintain the set temperature without using the auxiliary heat, lowering the outside temp will raise the balance point. Right?

  9. #22
    Join Date
    Sep 2004
    Posts
    3,157
    Norm--oh Norm

    I have to vote for "D" because I havnt learned about calculating the ratio yet and I dont understand how lowering the oat would raise the compression ratio

  10. #23
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,748
    [QUOTE]Originally posted by NormChris

    A heat pump is operating in the heating mode. The lower the outside air temperature, the

    a. more efficient the heat pump.
    b. higher the SEER rating.
    c. higher the compression ratio.
    d. lower the balance point.
    [/QUOTE




    e. happier i am i do not work on heat pumps

  11. #24
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,350
    Originally posted by jacob perkins
    Because suction pressure is much lower with a somewhat steady range of condensing pressures (in the heat mode)....
    Exactly. That's what I was getting at in my reply...you just did a better job cutting to the chase.

    I am a one single-moded thinker.I cant help it.Heating and cooling in the same paragraph confuses me.

    No problem. Everyone approaches the same thing a tad differently. Makes life interesting.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  12. #25
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,350

    Re: Blance Point

    Originally posted by pokerface
    Since the balance point is the temperature outside at which the unit cannot maintain the set temperature without using the auxiliary heat, lowering the outside temp will raise the balance point. Right?
    Balance point = heat loss of structure is equal to heat produced by heat pump w/o heat strips. Typically at a given outdoor ambient temperature is when balance point is reached.

    Below balance point, heat strips may be needed. Above balance point, may not be needed. Also, outdoor temp can be above balance point but heat strips still may kick on if space temp has dropped signficantly below setpoint that would cause second stage of thermostat to be activated.

    Lowering outdoor temp does not "raise" balance point (BP) as BP is at a fixed outdoor temp for the structure's heat loss rate to heat output of heat pump. Below BP, which translates to OAT below BP, heat pump BTU output diminishes. Above BP, heat pump BTU output is greater than heat loss of structure.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  13. #26
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,350
    Originally posted by ct2
    Norm--oh Norm

    I have to vote for "D" because I havnt learned about calculating the ratio yet and I dont understand how lowering the oat would raise the compression ratio
    Compression ratio = suction pressure in pounds per square inch absolute (psig + 14.7 @ sea level = psia) divided by discharge pressure in psia = compression ratio.

    As OAT drops, compression ratio will rise due to lower temperatures and pressures in outdoor coil (serving as an evaporator when the system is in heat mode), compared to fairly consistent discharge pressures as one would find when the system is in cooling mode. The wider the spread between suction and discharge pressures, the higher the compression ratio.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

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