M Night Time Condensation on Tarp and Tent Fabrics
by Mariah Walton
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The potential for condensation build-up on tents or tarps is an important concern when considering new equipment. Condensation occurs when the temperature of a fabric drops below the dew point of the surrounding air. This paper investigates the formation of condensation on a passive fabric - one that is not influenced by heat and moisture from humans. Understanding the formation of condensation on a passive fabric is the first step towards understanding condensation in more complex situations. In the sections below, I first review some of the fundamental concepts involved with the formation of condensation on fabrics and then present the results of an experimental investigation.
This study discusses the concept of water balance, so the reader is provided with a basic understanding of concepts fundamental to the interpretation of condensation data. Concepts discussed include humidity (absolute vs. relative), dew point, heat of condensation, and latent heat.
A discussion of heat balance is provided so the reader understands how and why condensation forms on shelter fabrics.
An experimental description and apparatus is provided, including a unique test shelter panel construction quilted using several different types of fabrics (double layered nylon, double layered coated nylon, mesh, single layered nylon, single layered coated nylon, single layer aluminized fabric, aluminized top/nylon bottom fabric, coated nylon top/aluminized bottom fabric, and waterproof-breathable fabric (Gore-Tex).
Results are provided, which discuss the influence of several factors on the formation of condensation to the different tent fabrics, including: temperature, overhead cover (i.e., clouds and trees), wind, humidity, elevation, pitch height, and of course, fabric type.
Interestingly, the data showed that cover had the greatest statistical impact on the difference between fabric surface and air temperatures. Other important factors included ground temperature and humidity. The importance of other factors, including differences between fabric surface and air temperatures, elevation, wind, etc., are also discussed in context.
This study is not intended to be a comprehensive treatise on the subject of condensation formation to lightweight shelter fabrics; rather, it provides important baseline data that highlight some of the important considerations for shelter design (in terms of fabric selection) and environmental factors that are controllable by the hiker (campsite selection and how a shelter might be pitched) that can be capitalized upon to minimize condensation formation.
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