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Title: Controlling building energy use by Overall Thermal Transfer Value (OTTV)
Authors: Chow, WK 
Issue Date: 2000
Source: Energy, 2000, v. 25, no. 5, p. 463-478
Abstract: Overall Thermal Transfer Value (OTTV) is used as a control parameter for building energy use in the Hong Kong Special Administrative Region (HKSAR). However, there are several approaches to determining the OTTV that produce quite different results. Four different methods for calculating OTTV are briefly reviewed and their formulation clarified in this paper. They are (1) the equations derived by Chow and Chan through extensive energy simulations, (2) the ASHRAE 90A-80 method, (3) the one recommended in the Hong Kong Code of Practice (HKCOP) published by the HKSAR Government, and (4) the basic definition of OTTV using data generated from computer simulations by TRACE 600. The OTTV of building envelopes is analyzed by studying the energy use of single-zone buildings with volumes varying from 4000 to 40,000 m3. Results of OTTV calculated from the four methods are compared and discussed. Method (1) is the simplest and easiest one to apply, and the results are found to be close to those simulated by computer programs. Finally, new approaches to total building energy control are described for consideration in the next revision of building energy codes.Ae Envelope area, including roof (m2)Af Floor area (m2)Ar Gross area of external walls (m2)Aw Gross area of roof (m2)top Total system operating time (h)hi Internal surface film thermal transmittance (W m-2 K-1)ho External surface film thermal transmittance (W m-2 K-1)k Thermal conductivity (W m-1 K-1)Qc Annual heat energy gain through building envelope (MWh)R Thermal resistance (m2 K W-1)SC Shading coefficient, SC for window, SCs for skylightSF Solar factor, SF for vertical surface, SFr for horizontal surface (W m-2)TDEQ Equivalent temperature difference, TDEQ for wall, TDEQr for roof (K)U U-value, Uf for fenestration, Ur for roof, Us for skylight, Uw for wall (W m-2 K-1)Vs Space volume (m3)α Absorptivity, αw for wall, αr for roofΣ SummationΔT Temperature difference between indoor and outdoor conditions (K)ASHRAE American Society of Heating, Refrigerating and Air-conditioning EngineersESM External Shading MultiplierOTTV Overall Thermal Transfer Value (W m-2)OTTV90w OTTV for wall, calculated by Eq. (5) (W m-2)OTTV90r OTTV for roof, calculated by Eq. (6) (W m-2)OTTV90e OTTV for envelope, calculated by Eq. (7) (W m-2)OTTVa OTTV calculated using Eq. (2) (W m-2)OTTVb Summer OTTV, calculated using Eq. (3) (W m-2)OTTVc OTTV for curtain-walling, calculated using Eq. (4) (W m-2)OTTVHKw OTTV for wall, calculated by Eq. (8) (W m-2)OTTVHKr OTTV for roof, calculated by Eq. (9) (W m-2)OTTVHKe OTTV for envelope, calculated by Eq. (10) (W m-2)OTTVTRACE OTTV simulated by TRACE 600 (W m-2)SSR Skylight-to-Roof RatioWWR Window-to-Wall Ratio.
Publisher: Pergamon Press
Journal: Energy 
ISSN: 0360-5442
EISSN: 1873-6785
DOI: 10.1016/S0360-5442(99)00079-1
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