Unmet Hours - RSS feedhttps://unmethours.com/questions/Question-and-Answer Resource for the Building Energy Modeling CommunityenThu, 27 Oct 2016 12:44:07 -0500SHR for Coil:Cooling:DX:Multispeedhttps://unmethours.com/question/20856/shr-for-coilcoolingdxmultispeed/ I have a set of SHR modifier curves that I would like to use with a Coil:Cooling:DX:Multispeed object. I've gone through all the fields of the object many times but I can't seem to find the ones dedicated to SHR modifier curves. I've checked the Engineering Manual for this object and it says that supposedly you can specify SHR curve fits for each speed:
> Each speed has a set of corresponding performance information at rated conditions along with curve fts for variations in total capacity, **SHR**, energy input ratio and part-load fraction to determine the performance of the unit at part-load conditions
Did I miss a field in the object? Is there a typo in the documentation? If yes, is there a reason why it is not possible to specify SHR modifier curves for this object?Thu, 27 Oct 2016 12:00:07 -0500https://unmethours.com/question/20856/shr-for-coilcoolingdxmultispeed/Answer by rraustad for <p>I have a set of SHR modifier curves that I would like to use with a Coil:Cooling:DX:Multispeed object. I've gone through all the fields of the object many times but I can't seem to find the ones dedicated to SHR modifier curves. I've checked the Engineering Manual for this object and it says that supposedly you can specify SHR curve fits for each speed:</p>
<blockquote>
<p>Each speed has a set of corresponding performance information at rated conditions along with curve fts for variations in total capacity, <strong>SHR</strong>, energy input ratio and part-load fraction to determine the performance of the unit at part-load conditions</p>
</blockquote>
<p>Did I miss a field in the object? Is there a typo in the documentation? If yes, is there a reason why it is not possible to specify SHR modifier curves for this object?</p>
https://unmethours.com/question/20856/shr-for-coilcoolingdxmultispeed/?answer=20858#post-id-20858This appears to be a typo. The sensible heat ratio is an integral part of the performance of a specific DX coil. Once the total capacity and air flow rate is known, the apparatus dew point temperature (the coil surface temperature) can be determined to find the operating SHR. Air flow rate also affects SHR indirectly through the Tcap function of flow fraction curve. So although SHR cannot be modified via a performance curve specific to SHR, the other available curves do indirectly adjust SHR according to the model assumptions.
The performance curves available for this object are:
A13, \field Speed 1 Total Cooling Capacity Function of Temperature Curve Name
A14, \field Speed 1 Total Cooling Capacity Function of Flow Fraction Curve Name
A15, \field Speed 1 Energy Input Ratio Function of Temperature Curve Name
A16, \field Speed 1 Energy Input Ratio Function of Flow Fraction Curve Name
A17, \field Speed 1 Part Load Fraction Correlation Curve Name
The SHR can be further modified via the latent degradation model if constant fan operating mode is used to describe the evaporation off the cooling coil when the compressor is off and the fan operates continuously. These inputs are:
N11, \field Speed 1 Nominal Time for Condensate Removal to Begin
N12, \field Speed 1 Ratio of Initial Moisture Evaporation Rate and Steady State Latent Capacity
N13, \field Speed 1 Maximum Cycling Rate
N14, \field Speed 1 Latent Capacity Time Constant
Thu, 27 Oct 2016 12:44:07 -0500https://unmethours.com/question/20856/shr-for-coilcoolingdxmultispeed/?answer=20858#post-id-20858