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Anthropogenic heat and its relation to building and urban climate in Inuvik, N. W. T. Nicol, Keith Sherman

Abstract

Previous studies involving energy utilization and climate have stressed the importance of anthropogenic energy release (i.e. that energy generated by human activities) on urban climate. The reverse influence, climate's effect on energy use, is less frequently discussed. This investigation examined the influence of various atmospheric parameters that act to create a space heating demand, and some of the climatological effects of the consequent anthropogenic heat release in the extreme case of an Arctic settlement in mid-winter. Inuvik, N.W.T. (68° 22', 133° 45') was chosen as the study site, primarily because of the settlement's centralized heating system which enabled the anthropogenic heat generation to be readily monitored. The measurement of anthropogenic heat spanned two spatial and temporal scales. Initially, the energy involved in the space heating (for the utilidor-served portion) of Inuvik is regressed against air temperature, wind speed, and solar energy establishing predictive energy-use equations for daily and hourly periods. The equations were well correlated (r²=0.90) for both periods, with temperature and wind speed being the most significant variables. It is suggested that once quantified, an energy-use equation might be a useful input to certain urban boundary layer models (e.g. Summers, 1965) which are capable of providing heat island intensities and mixing depths. On a smaller scale, heat loss from a single window surface was analyzed experimentally. The energy balance for an exterior window surface (at the Inuvik Research Laboratory) was obtained under varying atmospheric conditions (i .e. wind speeds and cloud cover). Wind speed was significant, in determining sensible heat transfer from the window surface, and values for the heat transfer coefficient are in good agreement with those of other workers. The controls on radiative and convection heat losses from windows are discussed in the light of the observational data. The potential of anthropogenic heat to modify the townsite climate of Inuvik is examined in two ways. Firstly, the influence of this energy is investigated in regard to its effect on the net long-wave radiation balance. Observations indicate that the townsite net long-wave radiation values were consistently more negative than rural measurements during January, 1975. It was considered that this was due to the greater emission of long-wave radiation from the "warmer" urban surface. A statistical link between urban and rural net long-wave radiation differences and township energy-use was obtained. This link further supports the argument that the greater urban radiation output is related to anthropogenic releases. Attempts to model clear sky counter-radiation revealed that the Idso and Jackson (1969) equation was most suitable. Secondly, the impact of the anthropogenic heat in altering the surface energy balance of Inuvik and its environs is investigated. The energy balance was assessed from both measurements and a numerical simulation model. Energy balance comparisons between the two methods are reasonable, as are the predicted and observed heat islands intensities. With cloudless skies, typical measured, townsite energy balance values (Jan. 1975) were: net long-wave radiation flux - -39 Wm⁻², sensible heat flux - -7 Wm⁻², and anthropogenic heat flux - 46 Wm⁻². The equivalent observed rural balance is: net. long-wave radiation flux - -32 Wm⁻² and sensible heat flux - -32 Wm⁻². In summary, the relation of urban climate to energy use is one of interaction rather than unidirectional, cause and effect. That is, climate initially forces an energy demand on an urban area. However this energy demand results in anthropogenic heat release which in turn modify the urban atmosphere. The creation of a warmer urban climate alters the energy demand slightly, creating a dynamic interaction with strong, mainly negative feedbacks.

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