THERMODYNAMICS Project - Medford - R600

Exported for Jianhao Li on Tue, 18 May 2021 21:23:51 GMT

Project - Medford - R600 Sign up for a team on Canvas. Sign up even if you wish to work alone.

Your project is to assess a vapor compression heat pump cycle on a daily basis over the course of year at a

location to be provided. The year of data provided is a leap year, hence there are 366 days. As a result of

analyzing the cycle over the course of an entire year, you must also analyze the cycle performance for that

part of the year during which it operates as an air conditioner.

You will be assigned the location and the refrigerant to employ in your cycle. You will only employ the four

components employed in a simple vapor compression heat pump/refrigeration cycle. Refer to Figure 10.3 in

the textbook.

Below is a link to access a video that explains ground-based heat pump.

https://www.energy.gov/energysaver/heat-and-cool/heat-pump-systems/geothermal-heat-pumps

Keep in mind, however, that you will be analyzing an air-based heat pump. This means you will be using air

temperatures as the cold thermal reservoir when the cycle acts as a heat pump and as the hot thermal

reservoir when the cycle acts as an air conditioning system.

You will be provided daily average temperatures as well as the average standard deviation of those daily

temperatures. This is the data on which your project are to be based and on which the project will be

graded. Assume a constant indoor temperature of 70 F.

Work the analyses in the order noted below. Read through the procedures prior to starting the project. Note

that if you elect not to follow the order of analyses recommended or elect not to follow the specific

instructions under each analyses, our ability to help you will be severely hampered.

Determining cooling days versus heating days in spreadsheet to be provided

It is easiest if you perform cooling day versus heating day predictions in the excel spreadsheet associated

with the location that you have been assigned. It is less confusing if you leave data in Fahrenheit for the

initial heating versus cooling day analysis. Take the average temperature and add to it twice the standard

deviation in temperature and subtract from that the temperature inside the house (70 F):

   T +avg 2T −stdev T indoor

If the value is less than zero, assume it to be a heating day. If the value is greater than zero, assume it to be a

cooling day. For heating days, use the following as the outdoor temperature:

   T =outdoor T −avg 2T stdev

For cooling days, use the following as the outdoor temperature: 

   T =outdoor T +avg 2T stdev

This will allow you to design to extremes, hence is termed the outdoor design temperature. 

Create a single column of Toutdoor in units of Fahrenheit. Convert this column to units of Celsius. Make sure

there are at LEAST 4 significant digits in this spreadsheet column. When you are ready (i.e., after you have developed and debugged your code for a single heating day and a single cooling day) copy and paste

this column into a parametric table in EES. 

Note that because you are designing based on a worst case scenario, rather than on the average

temperature, there will be a discontinuity in your data, hence in your plots, where you convert from heating

days to cooling days and vice versa.

Heating/cooling load assessment in EES

All analyses must be conducted in EES working in SI units. Include units for all variables. If a value has no

units, assign it units of [-].

Use the following set of equations to determine the rate at which heat enters or leaves the HOUSE. These

are called heating and cooling loads, respectively. Make sure to reference this to the appropriate heat into or out of the CYCLE. A schematic diagram with heat arrows crossing into and out of the house and into and

out of the cycle is a very good way to make this assessment.

  =Q̇house +Q̇convection Q̇radiation

where

  =Q̇convection UA(T −outdoor T )indoor

and

  =Q̇radiation 0.1 Q̇convection

Values of U and A are 0.006 kW/m2-oC and 4000 ft2, respectively. Neglect energy input to the house from

other appliances, people, etc.

Because we are designing a cycle based on the worst case outdoor conditions, i.e., the daylight temperature will be warmer than the outdoor design temperature on heating days and nighttime temperature will be cooler than the outdoor design temperature on cooling days, we should actually be doing this on a hourly basis. Rather than having 8784 lines in our parametric table, we will use a standard measure called the duty cycle to correct our computed heating/cooling loads.

What is a duty cycle? Heat pumps/air conditioners do not run constantly, unless they are undersize. They only run/cycle intermittently. Assume a linear variation in cycling where the system runs 20% of the time

when 

   T −indoor T =outdoor 60 Fo

during the heating period and runs 0% of the time when the temperature difference is zero. 

For cooling, assume the system runs 20% of the time (a duty cycle of 0.2) when the same temperature

difference is -20 F. Again the cycle duty should be 0 when the temperature difference is zero. Note that a

difference in oC or K does not equal the same difference in oF or R. 

In reality, the duty cycle only influences the power input, but we need a correction to the heat load, so we are using it in that capacity for this project. This is called the adjusted heating/cooling load.

Cycle Analysis in EES

Although you have been encouraged to write state points in arrays in previous assignments, you are

encouraged NOT to use P[1], h[1], etc. for pressures, enthalpies, etc. for this project. Leave as P_1, h_1, etc. It will be simpler to perform your parametric analysis.

Using SI system of units, ensure that your pressures in the evaporator and condenser are in units of kPa.

Use an isentropic compressor efficiency of 87%. Assume the cost of electricity is 9 cents per kWh.

Use a 5oC setpoint temperature for the evaporator and the condenser. This means you should set the

evaporator pressure to yield a saturation temperature 5 degrees lower than the low temperature reservoir.

The low temperature reservoir is the outdoors during heating (heat pump) and the indoors during cooling

(air conditioner). You should set the condenser pressure to yield a saturation temperature 5 degrees higher

than the high temperature reservoir. This means that your pressures are going to change on a daily basis.

These pressure will NOT be nice round numbers.

Baby steps

You are encouraged to work in incremental (baby) steps. Draw your system schematic. Label your state

points using standard convention. Write every equation on a sheet of paper before you sit down to code.

Start with a single heating day and make sure you can get the cycle to work as a heat pump. You can debug

using examples in the textbook and using the fluid employed in the examples. 

Next, expand the analysis to analyze a single cooling day. Check your the refrigeration (air conditioning)

cycle again using a textbook example. 

Then try a parametric table to analyze both states. Let the heating case serve as run 1 and the cooling case

serve as run 2. Then increase it to 5 heating cases and 5 cooling cases.

Once all is debugged, expand the parametric table to 366 runs and copy and paste the temperature data (in

oC) from the spreadsheet into the table and run the analysis. 

Plot the figures. Your results should fall within the limits specified for the axes (see below). You can also use

these limits to check the output of your single heating case and the single cooling case.

In the last step swap out the fluid. One easy way to swap fluids is to assign the variable sub$='R134a' and

use sub$ in lieu of the substance in the EES code. For example, h_1=enthalpy(sub$,T=T_1,P=P_1). Then all

you have to change is the name of the refrigerant in the assignment statement.

It will be nearly impossible to debug if you code everything at once, rather than debugging in stages. If you

visit me during my office hours, I will be asking to see the results of each of these stages.

Output

Run your final analysis on the OSU COE licensed version of EES. Access this either using Citrix or the method

posted as an announcement on Top Hat Community. Provide a single output file printed directly to a pdf

file from EES. Note that a pdf is the required file format. Do not alter the file in any way. Do not change the

default font or other options in EES. A default header should appear when you do this.

The first five lines of the EES file MUST follow the following format. 

Assume you signed up under Project 42 with another person with whom you completed the project. Your

and your team member's names are Ric Ocasek and Aretha Franklin. You were assigned Hood River as the

location and R407c as your refrigerant. You would write the following as the first 5 lines of your code. Note

the order of family name and first name as well as alphabetization of the team members. 

{Project 42}

{Hood River}

{R407c}

{Franklin, Aretha}

{Ocasek, Ric}

If you worked alone and your name is Joe Elliott, you signed up solo for Project 122, were also assigned

Hood River but with R717 as your refrigerant, you would write the following for the first 5 lines.

{Project 122}

{Hood River}

{R717}

{Elliott, Joe}

{N/A}

Select the following options when saving the file to a pdf.

equations with line numbers

formatted equations

solution 

parametric table (there should only be one and the format is as below)

all 3 plots (details below)

print in color 

page breaks

Format of parametric table (366 rows, 14 columns) 

column 1 - days (1 through 366)

column 2 - Toutdoor [C]

column 3 - Pevaporator [kPa]

column 4 - Pcondenser [kPa]

Image of instructions above

column 5 - duty cycle [-]

column 6 - COP [-]

column 7 - adjusted house heating/cooling load [kW] column 8 - mass flow rate [kg/s] 

column 9 - compressor power [kW]

column 10 - cost per day [$ or $/day]

column 11 - h1

column 12 - h2

column 13 - h3

column 14 - h4

Format of plots

Plots must include axes labels, a plot title (Plot 1, Plot 2, Plot 3) and a legend. Do not use lines to connect

data. Use only symbols for data. Use the axes ranges specified.

Plot 1

Day on x axis  [0,100, 400] - yes, even though there are only 366 days

Toutdoor on le� y axis - axis limits [-15, 10, 35] where [minimum, increment, maximum]     

Adjusted heating/cooling load on right y axis - axis limits [-25, 5, 15]

Plot 2

Day on x axis  [0,100, 400] - yes, even though there are only 366 days

Cost per day on le� y axis - axis limits [0, 1, 10] where [minimum, increment, maximum]         

COP on right y axis - axis limits [0, 5, 30]

Plot 3

Day on x axis  [0,100, 400] - yes, even though there are only 366 days

Evaporator pressure on le� y axis - axis limits [0, 250, 2000] (Use these even if your P are low)     

Condenser pressure on SAME LEFT y axis

Make sure to select the automatic update on your plots ensure they update when you change your fluid from R134a.

Output contingency plan

Make sure to select the two boxes noted by red arrows.

If you are absolutely unable to put the entire analysis, heating and cooling on the same parametric chart,

you can provide two separate files. One for heating and one for cooling. On the heating file, data for cooling

days should equal zero. On the cooling file, data for heating days should equal zero. Other than that, the

two files must be presented identically. 

Assignment submission

The assignment will be submitted in two parts.

1. The pdf file (exactly as specified above) must be uploaded to Canvas under assignments before the

deadline. Late uploads will incur a point penalty. This file accounts for a maximum of 80% of your

project grade. Maximum points require strict adherence to instructions, a well organized - well

documented code, accurate analyses, and accurate results for your design. Professionalism also plays

a factor. Note that well documented does not mean excessively documented. Providing excess

comments in codes can be as bad as providing too few comments.

2. Answer questions on this page (which will be updated with questions prior to the project deadline).

Make sure you have a version of your Canvas file submission handy. This accounts for 20% of your

grade. 

Both parts of the assignment must be submitted to earn a grade. Submission of one part without

submission of the other part results in a grade of zero.

Projects must be submitted on time for full credit consideration. Late projects will incur a penalty of 10%

every 8 hours, with no proration. This means that a project submitted one minute late earns the same

penalty as one that is submitted 7 hours and 59 minutes late. 

You will have two weeks to complete the project. By completing the assignment early you will be able to

avoid any last minute inconveniences, such as a power outage, that would result in a late submission.

General information and recommendations