Lecture Objectives:

• Finish boilers and furnaces

• Start with thermal storage systems

Thermal storage for adjustment production to consumption

We need a thermal storage somewhere in this system !

Thermal storage

• Store heat• 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 costsLower on-peak electrical consumption(kWh)Lower on-peak electrical demand (kW)

• Smaller equipment sizeSmaller chillerSmaller electrical service (A)

• Reduced installed costMay 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 tanksdiffuser geometry

Challenge:“Pull” large amount of energy withoutdisturbing stratification

Modeling

Write energy and mass balancer equation for each section

Installation of thermal storage system

DownstreamUpstream

• Increases chiller efficiency • Increases chiller capacity • Overall system efficiency ??? • Decreases storage capacity• Simplifies system layout• …..

• Decreases chiller efficiency• Decreases chiller capacityOverall system efficiency ???• Increases storage capacity•……• Does not allow chiller shut down!

Mixing vs Diverting Valves

Plumbing arrangement in primary system Primarily-OnlyPrimarily & Secondary

Plumbing arrangement in buildings (secondary systems)