Right Sizing

Major Points:

• Life-cycle cost analysis

• Diversity analysis

• Equipment heat gainanalysis

• Provide design coordination!
  

Life-Cycle Cost Analysis

Life-cycle cost (LCC) analysis is intended to be a rational, objective method for selecting the optimum systems for a laboratory facility.

• Assess economic consequences of any decision by comparing two or more alternatives with LCC analyses.
  
• Use simple payback analysis (cost of alternative/value of energy saved) during the early stages of design.
  
• Employ detailed LCC analysis as necessary; identifies and quantifies all factors that influence total system cost and operation.
  – Subjective factors such as fuel cost adjustments, component reliability, and maintenance costs can be included.

Diversity Factor Analysis

In large labs with good sash management practices, fume cupboards are only partially open at any one time; typically 40% to 70% the sashes are closed.

Right-size HVAC equipment includes a diversity factor to calculate a more “realistic” HVAC-system peak load.

Using a diversity factor:
– decreases operational and first costs,
– gives better system control,
– increases system stability, and
– reduces mechanical space requirements. 

Diversity can be also used for estimating plug loads.

Apply Diversity Carefully

For safety purposes exhaust systems and small, single-room laboratories should be sized for full 100% capacity.

Taking advantage of diversity is particularly valuable when retrofitting existing facilities where available space is limited.

Equipment Heat Gain Analysis

The ASHRAE HVAC Applications Handbook chapter on Laboratories states that heat gain 5-25 watts/ft sq. are common for laboratories with high concentrations of equipment.

Based on Labs21 Benchmarking data, heat gains are often over-estimated by a factor of two or more.

Actual measured energy data for equipment is preferred.

Over-Estimating Equipment Heat Gain

Many factors lead designers to over-estimate peak heat gain from equipment.

• Lab users are likely to be optimistic about the amount of equipment they will obtain.

• Exact equipment use is not known, so worst case conditions are assumed.

• Researchers and equipment vendors are accustomed to defining equipment power draw in full load or nameplate amperage, without adjusting for duty cycles.
  
•   To be certain future cooling loads are met, large safety factors are common.