Lecture Objectives: Answer question related to Project 1 Finish with thermal storage systems Learn about plumbing systems

Stratified chilled water tanks

Temperature and dynamics Temperature at outlet

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

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)

Other latent heat thermal storage systems (research is ongoing)

Construction and benefits Active Passive (wall)

Modeling (stratified tank) 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 capacity Overall system efficiency ??? Increases storage capacity …… Does not allow chiller shut down!

Plumbing Systems - Hydronic Terms Head loss Open-loop vs. closed loop Open System Closed System Pump h Cooling coil in AHU Chiller Pump

Is this open or closed system ? Cooling towers

Relationship between velocity in a pipe and pressure drop Δp ~ v 2 Δp = Constant × v 2 Δp [Pa or ft water ] v [m/s or fpm] larger pipe smaller pipe Required power (P) for the pump P = V × Δp P –power [W], V –volume flow rate [m 3 /s], v – velocity [m/s] Δp – pressure drop [Pa] Δp ~ v 2 (Δp ~ V 2 – when same pipe is used ) P ~ V × V 2 – when same pipe is used P ~ V 3 P 2 /P 1 = (V 2 /V 1 ) 3 For the same pipe When different pipe is used for the same flow rate: For the same flow rate V Reduction of D: D1D1 D 2 = D 1 /2 A 1 V 1 P 1 A 2 =1/2 2 A 1 V 2 =2 2 V 1 P 2 /P 1 = (D 1 /D 2 ) 4 - for the same flow rate or 50% smaller diameter of the pipe for the same flow rate wee have: 4 times larger velocity 16 times larger pressure drop and 16 times lager power for the pump

Head Loss

Fittings

Pumps Raise pressure and produce flow Main type Centrifugal Inline Base mounted Example of Turbine pump Reading (textbook) Page

Pump curves NPSHR = Net Positive Suction Head Required

Changing Pump Speed

Net Positive Suction Head (cavitation)

Curve for Multiple Pumps

System Curves A B ∆p V A+B Parallel A B A B ∆p V A+B A B Serial

Find a system curve for this plumbing configuration

Primary/Secondary and Tertiary Pumping (schematics A&B below)

System balancing BOILER HC2 AHU1 AHU2 HC1 pump 100 ft 1000 ft 2 gpm 10 gpm 10 ft