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    Correct way to interpret the water-to-air heat pump performace data (4 Posts)

  • Arez Arez @ 2:39 PM
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    Correct way to interpret the water-to-air heat pump performace data

    Dear all,

    I am involved with a project that is about numerical modeling of performance of a ground heat exchanger (or mistakenly called geothermal) attached to a water-to-air heat pump. In my model, I need to have a relatively accurate estimate of the following parameters:

    1- Heating and cooling loads
    2- Air flow rate
    3- Fluid flow rate
    4- Heating and cooling power requirement

    Questions:
    1. I wanted to know if it is a reasonable assumption to say that there is a linear relationship between the HP tonnage and all the above parameters? The reason I am asking is because I need to be able to give the software a range of different HP tonnage and subsequently a range of operating parameters that results from selection of a bigger or smaller pump. So, I need some sort of automatic reasonable data input to approximate the vicinity of each of the above parameters.

    2. My main issue is with sample performance data reported online. I don't seem to be able to make sense out of the HP Power requirements for each unit. I have copied the link to the performance data that I am looking at. I am concerned with the horizontal ground source data reported on page 26 of the manual as well as the related electrical data on page 49 for standard static motor.

    http://www.htseng.com/default/products/PID567/resources/McQuay%20Enfinity%20Catalog.pdf

    First of all, is the WATTS column the power requirement of the system? If yes, then why the ration of cooling/heating capacities to the WATTS does not equal COP in units larger than 009? Then, looking at page 49 for electrical data, I assume Watts=V (voltage)*I(amperes) to compare the results to the WATTS reported in ISO standard condition. The reported WATTS in table on page 26 are much higher than the wattage that I calculate from the voltage and amperage data?!

    Where am I getting this wrong? What is the correct power requirement for each unit, the one in the table right next to the capacity or the product of voltage and amperage? Why the COP calculation=Capacity/HP power does not give the reported COP values in heating and cooling?!!

    Appreciate your help. I am new to the HVAC world.
  • Empire Empire @ 7:14 PM
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    Boat load of info;

    While your question would take some time to completely answer, Here are a few things that are invaluable and aids in the calculations you seek;  These are engineering answers and will still take time to look them up.  Hope this helped.

    Manual "J" or right "J"
    CFM Ductulator
    B&G System Syzer calculator and,
    "Ugly's"  Electrical reference guide.
    Pump selection graph to choose your pump.

    Mike T.
    This post was edited by an admin on October 27, 2012 7:16 PM.
  • Housedoc Housedoc @ 6:31 AM
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    I hope this is what you're asking

    1 Heating and cooling loads for buildings are estimated using methodology set forth in ASHRAE Bookmof Fundamentals. If you don't want to know that much, the Cliff's notes versions are ACCA Manual J, 8th edition for residential and Manual N for commercial. Software is available for both tasks. However, learning to manipulate the software doesn't guarantee accuracy. One must understand the methodology to generate good numbers.good numbers are essential for proper equipment selection and meaningful simulation estimates.

    2. Airflow rates are determined by the required loads, the required sensible heat ratio and the performance of the equipment at design conditions.

    3. Fluid flow rates are determined by matching the building loads to the operating capacity if the equipment, considering the ground loop configuration, soil type, pressure drop, desired entering fluid temp and resultant temp change in through the loop.

    4. Power requirements are found on the data plates on the unit and circulators.

    Question #1 is a bit overly broad and non specific. If you're asking if there is a linear relationship between the product of the building loads and equipment selection, design airflow and fluid flow, then yes, because its the same procedure every time. If you're asking if a linear relationship allows short cuts to the process, then no. Enery building is different. If you're asking ig there is a linear relationship between the building loads, equipment capacity, flow rates, airflow and power requirements, yes, most of the time. Building loads are variable as well as sensible what ratios. We also build in different parts of the world. So, climates are different.

    Got to run before getting to #2. Maybe later....
  • Housedoc Housedoc @ 6:50 AM
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    Back again

    #2 page 29 shows the performance of the various size units based on a specific set of conditions as in entering air and fluid temps as detailed in the ISO standard noted on the table. This allows a designer to compare Acme unit with AAA's unit without any infusion of propaganda. All units are rated at the same conditions to level the playing field and give objective data.

    Page 49 shows operating parameters various input points. These extended details are necessary to select the right unit. If you use the same assumptions as the ISO ratings, the extended performance tables will show identical results, unless the standard adds watts for pumping power. Some do and some don't.

    Does this help?
    This post was edited by an admin on November 1, 2012 6:52 AM.
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