Dehumidification and cooling loads from ventilation air
Ninety-five years since Willis Carrier began the modern era of air-conditioning by dehumidifying a printing plant, industry is becoming more concerned with the importance of controlling humidity in buildings. In part, this concern stems from indoor air quality problems associated with excess moisture in AC systems. But more universally, the need for ventilation air has forced HVAC equipment originally optimized for high efficiency in removing sensible heat loads to remove high latent (moisture) loads. To assist cooling equipment and meet the challenge of larger ventilation loads, several technologies have become successful in commercial buildings. Newer technologies such as subcool/reheat and heat pipe reheat show promise. These increase latent capacity of cooling-based systems by reducing their sensible capacity. Also, desiccant wheels have traditionally provided deeper-drying capacity by using thermal energy to remove the latent load. Regardless of which mix of technologies is best for which applications, there is a need for a more effective way of thinking about the cooling loads created by ventilation air. It is clear from the literature that all too frequently, HVAC systems do not perform well unless the ventilation air loads have been effectively addressed at the original design stage. This article proposes an engineering shorthand, an annual load index for ventilation air to help improve the ability of HVAC systems to deal efficiently with the amount of fresh air industry has decided is useful for maintaining comfort in buildings. The proposed ventilation load index (VLI) is the load generated by one cubic foot per minute of fresh air brought from the weather to space-neutral conditions over the course of one year. It consists of two numbers, separating the load into dehumidification and cooling components: latent ton-hours per cfm per year + sensible ton-hours per cfm per year. The ventilation load index allows for quick comparisons between loads in different geographic locations. As a result, the index can help an engineer consider how the HVAC system design and equipment selection should vary according to climate and amount of outside air.
- OSTI ID:
- 20003828
- Journal Information:
- Energy Engineering, Journal Name: Energy Engineering Journal Issue: 6 Vol. 96; ISSN EENGDO; ISSN 0199-8595
- Country of Publication:
- United States
- Language:
- English
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