CASE08 · Manufacturing · HVAC
Resolving simultaneous heating and cooling in a semiconductor facility
AHU operating data revealed overlapping chilled-water and steam valve operation. Seasonal changes were applied first to general-purpose AHUs, while cleanroom systems were treated separately to protect production conditions.
01 · CASE ANALYSIS
Operating challenge
Repeated simultaneous opening of chilled-water and steam valves was observed in both general-purpose and cleanroom AHUs. Some cleanroom AHUs also showed chilled-water valve hunting and insufficient summer dehumidification.
Cleanroom temperature and humidity requirements made direct operating changes sensitive to production quality. General-purpose AHUs were therefore the first implementation boundary.
02 · CASE ANALYSIS
Data & analysis
The analysis used return, supply and room temperature/humidity and chilled-water, steam and humidification valve positions for six general-purpose AHUs and four cleanroom AHUs. AHU on/off signals, chiller-header temperatures, electricity, gas and monthly energy patterns supported the diagnosis.
Cooling and heating reductions were estimated from differences in valve positions using one week before and one week after the changes. The report applied an overall cooling-system COP of 2.0, a boiler efficiency of 95%, electricity at KRW 120/kWh and gas at KRW 35.5652/MJ. These are historical report assumptions.
| Period / boundary | Reported basis | Estimated cost saving |
|---|---|---|
| Summer, June–September | Cooling KRW 58.93m + heating KRW 26.28m | KRW 85.21 million |
| Winter, November–March | Cooling KRW 73.55m + heating −KRW 0.87m | KRW 72.69 million |
| Annual total, two general-purpose AHUs | Report’s annualized result | KRW 157.9 million/year |
03 · CASE ANALYSIS
Implemented measures
In summer, conflicting steam-valve operation was blocked; in winter, conflicting cooling-valve operation was blocked. Operating changes began on three general-purpose AHUs without production impact.
Cleanroom AHUs were analyzed and gradual valve-adjustment tests were proposed. The case does not claim that the same changes were directly implemented throughout the cleanroom systems.
04 · CASE ANALYSIS
Results & interpretation
The annual estimate combines two general-purpose AHUs; one AHU with negligible effect was excluded. Summer and winter estimates were annualized using monthly energy-consumption shares.
The reported total is approximately KRW 157.9 million/year. It is an annualized estimate derived from operating comparisons, not a full-year directly measured saving. Current prices or different COP and boiler-efficiency assumptions would change the estimate.
05 · CASE ANALYSIS
Measurement & verification
Compare valve behavior and delivered service under comparable seasonal conditions. Assess temperature, humidity and dehumidification alongside energy, and verify energy reductions within a clearly defined cooling/heating boundary.
Do not transfer an AHU strategy to a cleanroom without confirming its production and environmental requirements.
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