[TRNSYS-users] Questions about Type941 source code

[Zhe Li]

Dear David,

 

Thanks very much for your prompt answer.

 

I understand your first point. For the circumstance I am working with, the
relative humidity is actually not necessary. Hence for calculations concern,
I don’t have to have it. 

 

For the second point, What I am trying to ask is what will happen if the
inlet temperature is 4.7oC and inlet water temperature is 27.5oC. The file
contains the fraction of capacity and power: 0.759 0.787 at T_air=2.2oC and
T_water_in = 25oC, and 1.048 0.938 at T_air= 7.2oC and T-water_in=30oC. The
required value is actually half of the value in the data. How would the
interpolation routine deal with it or similar circumstance? 

 

Thank you very much for your help. 

 

Zhe Li

 

From: David BRADLEY [mailto:d.bradley at tess-inc.com] 
Sent: 22 April 2013 16:12
To: Zhe Li
Cc: trnsys-users at cae.wisc.edu
Subject: Re: Questions about Type941 source code

 

Dear Zhe,
  I have seen air(source)-to-water heat pumps used in two kinds of
applications. In one, the air side is outside the conditioned space and you
are correct that in this circumstance, the RH of the outlet air is probably
not going to be used for anything. In the other type of application,
however, the air side is in a conditioned space (for example there are
devices called heat pump water heaters that sit on top of a water tank; they
keep the water tank hot but in the process they cool (and dehumidify) the
air near the tank. In this case it is important to know what happens on the
air side. 

  You are correct that the data cannot be extrapolated beyond the range
given in the file. If you give the heat pump entering conditions that are
below the range, the model will get the capacity and power of the closest
point (ie the bottom of the range). The case is similar for the top of the
range; the interpolation routine will find the closest available point. If
you want to be more rigorous about your calculations, you can put additional
data points into the file that show a 0 capacity and 0 power draw for the
device if it gets very cold or very hot inlet conditions.
Kind regards,
 David





On 4/22/2013 09:19, Zhe Li wrote:

Dear David,

 

Thank you very much for your previous reply. 

 

I am hoping you can clarify some of my confusions with this source
code(Type941). I have studied this Type941 source code carefully. From my
understanding is the outlet fluid temperature is not calculated from the
amount of heat contained in the air. The Capacity and Power is worked out
completely depending on the Rated Catalog Performance using the hourly
ambient temperature and temperature of the fluid. So why does the relative
humidity require at all? Is it only used to calculate the inlet and the
outlet air properties which is not going to affect the fluid temperature in
any way?  

 

As I understand from previous questions, the interpolation Rated Catalog
Performance data could not be extrapolated from beyond the range provided?
However, what would be the calculation (selection) if the inlet ambient
temperature is 5oC and inlet water temperature is 27.5oC, how would the
fraction capacity and power calculated out (decided)? 

 

Thank you very much for your kind answer.

 

Zhe Li

 

From: David BRADLEY [mailto:d.bradley at tess-inc.com] 
Sent: 19 April 2013 18:04
To: TRNSYS users mailing list at the Solar Energy Lab, UW-Madison
Cc: Zhe Li
Subject: Re: [TRNSYS-users] Question about a line in Type941 source code

 

Zhe,
  lps_air is the volumetric flow rate of the air (in liters per second) and
rho_air_dry_in is the density (in kg/m3) of the dry air at the heat pump
inlet temperature.
Best,
 David




On 4/19/2013 11:11, Zhe Li wrote:

Dear All,

 

Thank you for your time.

 

I am trying to understand how TRNSYS calculates power output from this
air-water heat pumps (Type941).

 

I am stuck in a line which I don’t know what the two terms are standing for?


 

! Determine the dry air mass flow rate

Flow_air = lps_air*3.6*rho_air_dry_in 

 

Could somebody let me know what are the lps_air and rho_air_dry_in standing
for?

 

I hope I did not break TRNSYS source code rule by asking this question. 

 

Thank you for your help in advance.

 

Zhe Li 


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***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI  53703 USA
 
P:+1.608.274.2577
F:+1.608.278.1475
d.bradley at tess-inc.com
 
http://www.tess-inc.com
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-- 
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI  53703 USA
 
P:+1.608.274.2577
F:+1.608.278.1475
d.bradley at tess-inc.com
 
http://www.tess-inc.com
http://www.trnsys.com


Tá an teachtaireacht seo scanta ó thaobh ábhar agus víreas ag Seirbhís Scanta Ríomhphost de chuid Seirbhísí Faisnéise, ITBÁC agus meastar í a bheith slán.  http://www.dit.ie

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