Announcement EWRE Seminar Series Presents: Monday, April 24, 2017, 12:00 – 1:00 pm CPE 2.212 How Much Carbon Dioxide Do People Emit and Who Cares?” Andrew Persily National Institute of Standards and Technology 100 Bureau Drive, MS8600 Gaithersburg, Maryland USA andyp@nist.gov

Lecture Objectives: Learn about Mat lab equation solving Discuss Take Home Exam Finish with Absorption Cooling Systems Learn about thermal storage systems

MATLAB BASICS Hongwan Li hl24246@utexas.edu

Goals  

Import data from Excel From text

Define variables and time step

Loop for loop to repeat specified number of times

Solve equations

fsolve Nonlinear system solver Solves a problem specified by F(x) = 0 x is a vector or a matrix Syntax: x = fsolve(fun,x0) starts at x0 and tries to solve the equations fun(x) = 0, an array of zeros x = fsolve(fun,x0,options) solves the equations with the optimization options specified in options [x,fval] = fsolve(fun,x0) returns the value of the objective function fun at the solution x

Solve equations Options: Display-'off' or 'none' displays no output. 'iter' displays output at each iteration, and gives the default exit message. MaxFunEvals- Maximum number of function evaluations allowed, a positive integer. TolFun-The termination tolerance for the function value. The default value is 1.e-4.

Solve equations aw+bv+cz=13 5aw-6cv=20 w-2bv-7z=18 A*X=B    

Export data to excel

Plot

Plot

LiBr-H2O Systems

LiBr-H2O Systems

Twine vessel LiBr-H2O Systems

Useful information about LiBr absorption chiller http://www.cibse.org/content/documents/Groups/CHP/Datasheet%207%20-%20Absorption%20Cooling.pdf Practical Tips for Implementation of absorption chillers Identify and resolve any pre-existing problems with a cooling system, heat rejection system, water treatment etc, before installing an absorption chiller, or it may be unfairly blamed. Select an absorption chiller for full load operation (by the incorporation of thermal stores if necessary) as COP will drop by up to 33% at part-load. Consider VSD control of absorbent pump to improve the COP at low load. Consider access and floor-loading (typical 2 MW Double-effect steam chiller 12.5 tons empty, 16.7 tones operating). Ensure ambient of temperature of at least 5°C in chiller room to prevent crystallization. http://www.climatewell.com/index.html#/applications/solar-cooling

System with no pump (Platen-Munter system) H2O-NH3 + hydrogen http://www.youtube.com/watch?v=34K61ECbGD4

Thermal storage for adjustment production to consumption We need a thermal storage somewhere in this system !

Thermal storage Store heat Store cooling energy Many issues to consider (∆T, pressure, losses,…. ) Store cooling energy Chilled water For cooling condenser For use in AHU (cooling coils) Ice storage Compact but… Other materials (PCMs) that change phase the temperature we need in cooling coils Many advantages, but disadvantages too!

On-Peak and Off-Peak Periods This profile depends on the type of building(s) !

Chilled water tank Use of stored cooling energy Store Use

Which one is better ? Depends on what you want to achieve: Peak electric power reduction Capacity reduction …..

Downsizing the Chiller Lower utility costs Lower on-peak electrical consumption(kWh) Lower on-peak electrical demand (kW) Smaller equipment size Smaller chiller Smaller electrical service (A) Reduced installed cost May qualify for utility rebates or other incentives

Sizing storage system (use Annual Cooling-Load Profile) How often you need to use it? What are the cost-benefit curves ? What is the optimum size ?

Ice Storage Tank Many issues ! …. As freezing progresses progress the ice becomes thicker and significantly impedes heat transfer

Open Ice Storage Tank Also issues ! …..

Fluid Flow Rate and Freeze ΔT

Impact on Chiller Efficiency

PCMs A. Sharma et al. / Renewable and Sustainable Energy Reviews 13 (2009) http://www.docunator.com/bigdata/1/1367142535_c566e7d75e/reviewexample2.pdf

Other latent heat thermal storage systems (research is ongoing)

Construction and benefits Active Passive (wall)

Stratified chilled water tanks

Temperature and dynamics Temperature at outlet during the changing cycle of the tanks

Stratified chilled water tanks diffuser geometry Challenge: “Pull” large amount of energy without disturbing stratification

Modeling Write energy and mass balancer equation for each section

Installation of thermal storage system Upstream Downstream • Increases chiller efficiency • Increases chiller capacity • Overall system efficiency ??? • Decreases storage capacity • Simplifies system layout • ….. • Decreases chiller efficiency • Decreases chiller capacity Overall system efficiency ??? • Increases storage capacity •…… • Does not allow chiller shut down!