Central Plants And Cogeneration

Cogeneration and Central Plants – Harvard Green Campus Initiative – 8.26.08

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Two Guidance Documents:Two Guidance Documents:

CHP Calculation Methodology for LEED-NC v2.2 EA Credit 1

Required Treatment of District Thermal Energy in LEED-NC version 2.2 and LEED for Schools


CHP Calculation CHP Calculation Methodology for Methodology for LEEDLEED--NC v2.2 EA NC v2.2 EA

Credit 1Credit 1

November 2005November 2005




Case 1, Same Ownership, CHP in Case 1, Same Ownership, CHP in Building:Building:

Baseline design uses backup energy source of design or electricity

Treat electricity and heat used in the building as “free”

Charge standard rate for fuel

If extra electricity is sold, treat extra fuel as “process” in base and design case - treat heat generated as “free” in design case



Considerations for Considerations for Simulation/Calculation:Simulation/Calculation:

PRM requires hourly calculation of performance, either directly through simulation or manually through pos-processing of results

It may be possible to conduct calculation on annual basis if rate impacts are insignificant



Case 2, Different Ownership, CHP in Case 2, Different Ownership, CHP in Building:Building:

Same as Case 1

Baseline design uses electricity

Treat electricity and heat used in the building as “free”

Charge standard rate for fuel

If electricity is sold, treat fuel as “process”in both & heat as “free” in design case



Case 3 & 4, District CHP:Case 3 & 4, District CHP:

Essentially same as Case 1 & 2

Design utilizes a “virtual” CHP in building

If using all electricity associated w/thermal energy then fuel charged to design at standard rate & heat & electricity free

If extra electricity associated w/thermal energy then additional fuel charged to both as “process” and heat treated as free



CHP Systems Qualifications:CHP Systems Qualifications:

Annual CHP efficiency must be at least 60%

Must validate environmental performance w/narrative addressing emissions compared to natural gas boiler & electric chiller

Design building must meet EAp2 w/o CHP

To qualify for Case 4, project must:Have 10 year + commitment to purchase thermal output

Must be reliant on district system for 90% of thermal energy



Required Treatment of Required Treatment of District Thermal District Thermal

Energy in LEEDEnergy in LEED--NC NC version 2.2 and LEED version 2.2 and LEED

for Schoolsfor Schools

May 28, 2008May 28, 2008


Commissioning:Commissioning:

EAp1 – All upstream equipment is excluded

EAc2 – All downstream equipment is included

All upstream equipment is included if:Project greater than 50,000 sf

DES provides > 20% of annual energy cost

Building is pursuing EAc1 points beyond minimum w/modeling

OR

Project is 50% or more of DES connected or expected load

Required Treatment of District Thermal Energy in LEED-NC v2.2



Minimum Energy Performance:Minimum Energy Performance:

Must be compliant w/EAp2 w/o DES

Either prescriptive path or performance path:“Building Stand Alone” model

OR

Energy Cost Budget method



EAc1 EAc1 -- 2 Point Requirement:2 Point Requirement:

Prescriptive options w/o DES (unless required by reference standard)

Performance Option – Met w/o DEF –Appendix G w/DES specific edits – “Step 1”



EAc1 EAc1 -- Beyond 2 Point Requirement:Beyond 2 Point Requirement:

Prescriptive options w/ or w/o DES as required by reference standard

Performance Option – Include DES –Appendix G w/DES specific edits – “Step 2”



Step 1 Step 1 –– Building Stand Alone:Building Stand Alone:

Downstream equipment only – Energy source is purchased in design and baseline –Baseline HVAC edited as appropriate





Step 2 Step 2 –– Aggregate Building / DES:Aggregate Building / DES:

Downstream equipment & DES – Only for projects pursuing more than 2 points –Virtual DES plant for Design compared to code-compliant on-site plant for Baseline –Design is different than Appendix G, Baseline as instructed in App. G



Step 2 Step 2 –– Aggregate Building / DES:Aggregate Building / DES:



Modeling Design DES Heating:Modeling Design DES Heating:

Model Design building w/virtual heating plant w/same seasonal heating efficiency as entire upstream DES heating system

Derived from monitored data or engineering analysis

OK to model DES plant according to Appendix G

DES plant always modeled as total, entire unit



Modeling Design DES Cooling:Modeling Design DES Cooling:

Model Design building w/virtual chiller plant w/same seasonal cooling efficiency as entire upstream DES cooling system

Derived from monitored data or engineering analysis, including separate local 2° or 3°pumps if proposed

OK to model DES plant according to Appendix G

DES plant always modeled as total, entire unit



Default Efficiencies:Default Efficiencies:

Actual efficiencies preferred

OK to use following defaults (conservative):

DES heating – 70% (Higher Heating Value) for total boiler plant efficiency

DES cooling – COP of 4.4 for total cooling plant efficiency

Distribution losses – chilled water = 5%; hot water = 10%; closed loop steam = 15%; open loop steam = 25%



EAc1 Modeling:EAc1 Modeling:

Initial run to determine points w/o DES

Perform 2nd run w/ DES (including transmission & distribution loss)

Upload template w/Step 1 results as back-up

Upload template w/Step 2 as actual

EAc1 points achievable in Step 2 is limited to 4 additional beyond Step 1

Provide narrative of DES performance & modeling



Measurement and Verification:Measurement and Verification:

EAc5 – All downstream equipment is included

All upstream equipment is included if:Project greater than 50,000 sf

DES provides > 20% of annual energy cost

Building is pursuing EAc1 points beyond minimum w/modeling

OR

Project is 50% or more of DES connected or expected load



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