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
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
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
_______________________________________________
TRNSYS-users mailing list
TRNSYS-users@cae.wisc.edu
https://mailman.cae.wisc.edu/listinfo/trnsys-users
--
***************************
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
--
***************************
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