Re: [EnergyPlus_Support] DX Cooling coil single speed

Convection heat transfer is equal to the heat transfer across the surface and can be easily calculated using the u-value of the surface including film resistances in W/(m2*K).

The problem is that the film resistances change at each time step due to changing convection coefficients. Depending on what algorithm you chose to use (TARP, DOE, etc.) these are calculated for each surface using parameters such as orientation, local air velocity assumptions, volume aspect ratios, etc.

Also, the energy transfer can use a conduction FiniteDifference (condFD) method or CTF (default) method to take capacitive effects into account.

Additionally, other equipment may be defined that either transfer energy directly to the air node via convection or to all the surfaces first which in turn changes their surface temperatures and heat transfer across them.

Again, there are several things going on that converge on a solution. This is exactly why we use EnergyPlus. Don't calculate this with Matlab, instead feed the results of the heat transfers from e+ to Matlab if you require them.

On 6 Jul 2016 3:27 pm, "sandip gupta sandipgupta_nh@xxxxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:

Â

Dear sir,

Actually I am desigining a controller in matlab and through BCVTB I am sending the set point to E+. Now Most of the variables I am using from reporting variable. The only problem I am now facing is with calculation of
Â ZSF1:Zone Air Heat Balance Surface Convection Rate [W] and Â Air Heat Balance Outdoor Air Transfer Rate [W].
Can u help me with the related formulas used to calculate the above values. So that I can develop a suitable logic.

Regards,
--------------------------------------------
On Wed, 6/7/16, Jim Dirkes jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:

Subject: Re: [EnergyPlus_Support] DX Cooling coil single speed
To: "EnergyPlus_Support@xxxxxxxxxxxxxxx" <EnergyPlus_Support@xxxxxxxxxxxxxxx>
Date: Wednesday, 6 July, 2016, 6:09 PM

Â

Sandip,Have you
reported Output:Variables such as:Output:Variable,*,Cooling Coil
Electric Power,hourly; !- HVAC Average [W]Output:Variable,*,Cooling Coil Sensible Cooling
Rate,hourly; !- HVAC Average [W]
Another consideration is
to create Meter:Custom for specific
variables.
These may make your
evaluation simpler than using manual
calculations.Â
On Tue, Jul 5, 2016 at 4:32
PM, sandip gupta sandipgupta_nh@xxxxxxxxxxx
[EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx>
wrote:

Â

Dear Sir,

Thank you for your kind reply.

My main aim is to find the relation between Power
consumption by HVAC system for a given desired room
temperature and outdoor room temperature.I have already used
the performance curve to get the power consumption using

Q.total=Q.total.rated*EIR*RTF

Where RTF=PLR/PLF

and PLR=actual sensible cooling load /steady state sensible
cooling rate

What is the formula to calculate actual sensible cooling
load and steady state sensible cooling rate where can I find
this values is reporting XLS sheet.

How actual sensible cooling load and steady state sensible
cooling rate are related to Desired Set Point Temperature
and and Outdoor temperature.

With Regards,

Sandip Gupta

--------------------------------------------

On Wed, 6/7/16, Jean Marais jeannieboef@xxxxxxxxx
[EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx>
wrote:

Subject: Re: [EnergyPlus_Support] DX Cooling coil single
speed

To: EnergyPlus_Support@xxxxxxxxxxxxxxx

Date: Wednesday, 6 July, 2016, 1:06 AM

Â

Dear Sandip,

DX equipment models mostly use a set of 4

curves that are generated using regression analysis from
a

matrix of performance data provided by the manufacturer.

This matrix describes how the equipment performs under a

wide variety of different operating conditions. The
curves

are each in their own right normalized around a set of

"rating point" values.

There are two tools available that I have seen

to help you setup (and possibly understand better) the

performance curves in conjunction with appropriate
rating

point values (they go hand in hand). One is a
spreadsheet

tool that comes with e+ and can usually be found in your

launch bar. The other is from DesignBuilder. I use my
own,

but only I understand how it works.

Be forewarned that this topic is probably the

most advanced that the non-source-code writing
simulation

community can come up against. If you are a beginner e+

user, my advice would be NOT to start with the most
complex

issues first. If you have gained a basic understanding
about

part-load (part of "rated full load")
performance

together with the other factors influencing HVAC
performance

(like the humidity in the air and the temperatures of
both

air and cooling medium, as well as bypass factor) that

should be enough for now.

The equation you wrote is one of several that

are solved simultaneously using algorithms that converge
on

a solution. I'm sorry there is no easy answer. The

interdependencies are simply too complex to solve by

hand.

Perhaps you state what you wish your model

should demonstrate. Then state what you have done and
what

you observed, followed by what you cannot interperate or

generate for results.

Kindly yours,

On 5 Jul 2016 2:15 pm,

"sandip gupta sandipgupta_nh@xxxxxxxxxxx

[EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx>

wrote:

Â

Dear sir,'

While calculating the power consumption of a
DX

Cooling Coil Single Speed.

Step 1: Total Cooling Capacity as a function of
temperature

is calculated. Here from where does the Wet Bulb
temperature

comes from is it the sensor value.

Step 2: Total Cooling Capacity as a function of flow

fraction is calculated.

Step 3: Qtotal = Qtotal,rated * (TotCapTempModFac) *

(TotCapFFModFac) is calculated but from where do we get

Qtotal,rated. Pls help.

EnergyPlus? Version 8.5 Documentation Engineering

Reference Page Number 785 calculations.

Please help me out how to calculate the power consumption
of

HVAC system for different set point temperature. Does
the

above calculations satisfy my requirements.

I would be very very thankful to you if you kindly solve
my

doubts and problems.

With Warm Regards,

Sandip Gupta.

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--
James V Dirkes II, PE,
BEMP, LEED AP
CEO/President
The Building Performance Team Inc.
1631 Acacia Dr, GR, Mi 49504

Direct: 616.450.8653
jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx

Website l Â LinkedInÂ |
May

2016 ASHRAE Journal article on energy modeling

Either I win ? or I learn.

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