[TRNSYS-users] Questions about Type941 source code

[David BRADLEY]

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  <mailto:d.bradley at tess-inc.com>
>   
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>
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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

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