Methodology for the Evaluation of Natural Ventilation in ... - Cham

energy consumption and reduced first cost with ventilation equipment, but also in terms of theoccupant environment. Occupant comfort, though difficult to quantitatively measure, has beenevaluated through occupant surveys such as the PROBE studies (Bordass 2001). It has beenfound that the indoor temperature associated with thermal comfort of occupants has a largerrange in naturally ventilated buildings (Braeger and de Dear 2000), extending the range ofexterior temperatures at which natural ventilation is usable. The interior temperature is only oneaspect of the indoor environment, which includes air velocities and surface temperatures as well.In the design of naturally ventilated buildings, concern over the disturbing of papers due to highair velocities is a factor, but slightly higher velocities can also help in maintaining comfort withhigher internal temperatures. With slight increases in velocities, from 0.1 m/s to 0.25 m/s,occupants can tolerate a temperature increase of 3.6°C without any additional discomfort(Chandra et al 1986). For air velocities within the occupied space up to 0.4m/s occupants cantolerate interior temperatures of 28°C or 30°C as long as there are cooler surface temperatures onsurrounding walls, floors or ceilings (Allard 2002). Cooler surface temperatures can be achievedthrough proper use of thermal mass in the building design. Passively cooled and ventilatedenvironments have increased occupant satisfaction when occupants have the ability, or perceivedability, to control their own environment through the use of operable windows (Jones and West2001).The location of the building affects its performance as well. Climate influences the feasibilityand usage period of natural ventilation as a means to cool a building. Buildings in temperateclimates can use natural ventilation for most of the cooling season, May through October. Inclimates with a wider temperature range, including hot summers, passive cooling is stillapplicable, but greater attention to detail and design characteristics must be made. Lechner(1991) divided the United States into 17 different climate regions, based on maximum, minimumand average monthly temperatures, humidity, wind, sunshine and degree-days. Of the 17climates identified, 12 regions could benefit from natural ventilation, at least for a portion of thecooling period (Jones and West 2001).1.1 Building Energy UseIn temperate climates, the energy consumption required to cool and ventilate a building can bereduced by incorporating natural ventilation in the building design, though it is not often done. Inthe United Kingdom (UK), which has a climate suitable for naturally ventilated buildings, only ahandful of naturally ventilated commercial office buildings exist. The number is even less in theUnited States (US). Thirteen percent of the UK total energy consumption is used in the servicesector, which includes retail buildings. Of the 13 percent, 61 percent is consumed by the privatecommercial sector (DTI 2004), or commercial office buildings. Thus, commercial buildingsconsumed 7.9 percent of total energy used in the UK, as compared to 17 percent of the totalenergy usage consumed by commercial buildings in the US (EIA 2004). Though heating makesup most of the energy usage both in the US and UK, cooling energy is also a significant portion,representing almost 10 percent of all energy usage for commercial buildings (DTI 2004). In theUS, only 3 percent of commercial office buildings do not have air-conditioning. The breakdownof energy usage by sub-system for commercial office buildings in both the US and the UK ispresented in Table 1. The majority of the energy is used for heating, cooling, and ventilatingoccupied spaces. The US tends to have better envelope systems, but not necessarily highefficiency lighting or lighting controls. The UK, on the other hand, is known for its under-16