Re: [TRNSYS-users] Questions about Type941 source code

[David BRADLEY <d.bradley@tess-inc.com>]

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@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@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
This message has been scanned for content and viruses by the DIT Information Services E-Mail Scanning Service, and is believed to be clean. http://www.dit.ie

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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@tess-inc.com

http://www.tess-inc.com
http://www.trnsys.com