Theoretical Minimum Thermal Load in Buildings

Space conditioning for thermal comfort within buildings is one of the largest sources greenhouse gas emissions globally, creating an urgent need to realize deep energy reductions in this service meet climate goals. Our current approach providing relies on large spaces. In perspective, we show that inherently inefficient by introducing and calculating TMTL needed keep building occupants thermally comfortable. The approached when space volume aligns with immediate occupied individual. We such could deliver 10× use homes US. To investigate near-term solutions approaching TMTL, develop a simple approximate model calculate savings from increasing zonal control homes. number zones 10 modest temperature setbacks can up 70% reduction. highlight technologies available today facilitate increased control. also identify long-term technology development needs, highlighting research supports TMTL. Specifically, advances needs adaptive clothing, radiative heating, storage combined switches further Building cooling heating accounts portion total global requires commensurate amounts resources, which contribute significantly warming. Traditionally, addressing issue has meant improving efficiency equipment supplying energy, reducing envelope heat transfer, air infiltration. However, already reaching practical limits. explore (1) how reduce load theoretically (2) achieve reduction dramatically lower required support loads practically. First, discuss our framework developed theoretical minimum (TMTL) buildings. analysis shows are more than order magnitude higher introduce formula load, majority benefits be achieved fewer zones. Then, pros cons various approaches strategies conclude perspective some longer-term R&D ideas, as clothing help while additional benefit interacting renewable grid future. limit often viewed lens maximizing used demand. While realized substantial cost benefits, it only addresses half problem. Here, examine fundamental limits demand, transform unlock far beyond what was previously imagined. Nowhere change focus (thermal energy) premise why (i.e., occupant comfort) and, doing so, physical This presents new baseline highlights associated opportunities. Heating directly attributed 10% consumption anthropogenic CO2 emissions.1Ürge-Vorsatz D. Cabeza L.F. Serrano S. Barreneche C. Petrichenko K. trends drivers buildings.Renew. Sustain. Energy Rev. 2015; 41: 85-98Crossref Scopus (427) Google Scholar Current project share attributable will continue grow coming years, forecast increase globally 50% demand.2Editorial on.Nat. Energy. 2016; 1: 16193Crossref (7) For example, developing countries, air-conditioning demand expected >4.5x.3Davis L.W. Gertler P.J. Contribution adoption future under warming.Proc. Natl. Acad. Sci. U. A. 112: 5962-5967Crossref PubMed (248) Biardeau et al.4Biardeau L.T. Davis P. 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Given problem, way think about needed. community traditionally concentrated its supply transfer across through conduction well focused optimizing coefficient performance (COP) ACs/heat fuel utilization (AFUE) residential furnaces. Improving COP captivated scientists practitioners decades, governed Carnot deeply rooted second law thermodynamics.7Briley G. A history refrigeration.ASHRAE J. 2004; 46: S31-S34Google Similarly, using first thermodynamics benchmark, been able AFUE natural-gas-burning furnaces greater 90%, meaning 90% enthalpy natural transferred into heat.8Wheeler 1990s: technological breakthroughs efficiencies.Air Cond. Heat. Refrig. News. 2001; 214: 78https://www.achrnews.com/articles/87036-the-1990s-technological-breakthroughs-and-higher-efficienciesGoogle believe area investigation whether must provide comfort. 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Knowledge opportunities dramatic influence most important fastest growing services worldwide: concept researchers practitioners. material scientist currently next-generation textile materials personalized cooling/heating now determine metrics Additionally, system design distributed instead centralized ventilating, [HVAC] systems). determined considering primary purpose delivering buildings—to occupants. paradigm entire/partial individual (see Figure 1). sufficient occupant, defined maintain human body 37°C boundary conditions properties. framework, no actively supplied nor removed via HVAC system. Fundamentally, healthy temperature. define Human well-studied topic15Van Hoof Forty years Fanger’s comfort: all?.Indoor Air. 2008; 18: 182-201Crossref (407) serves basis widely standards like ANSI/ASHRAE Standard 5516ASHRAEANSI/ASHRAE 55–2016: Thermal Environmental Conditions Occupancy.2016Google ISO 7730.17International standard 7730, Third Edition. (2005-11-15).Google fundamentally balance around people; transfers calculated metabolism, activity levels, humidity, resulting calculation, statistical correlations people’s perception comfort, method assess prescribed “comfortable” average person. does address amount added or turn “uncomfortable” conditions. practice, achieving typically accomplished changing themselves (most temperature) create environment. means whole part cooled heated, leads contents, including unoccupied parts building. results much minimally Recent localized cooling18U.S. Advanced Research Projects Agency – (ARPA-E)Delivering efficient local amenities (DELTA).https://arpa-e.energy.gov/technologies/programs/delta#:∼:text=Delivering%20Efficient%20Local%20Thermal%20Amenities&text=ARPA%2DE's%20DELTA%20projects%20include,reductions%20in%20greenhouse%20gas%20emissionsDate: 2014Google initial step toward maintaining minimum, achievable addressed. personal hotly debated topic;19Wang Z. de Dear R. Luo Lin B. 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McGraw-Hill, 1972Google QSkin, QRespiration_L, QRespiration_D, QSweat, QRadiation, QConvection, follows:(1)Heat (QSkin) water diffusion skin QSkin=hwm(psk−pb), where hw latent vaporization water, m permeance skin, psk saturated vapor pressure pb TBuilding RHBuilding.(2)Breathing (QRespiration_L) sensible (QRespiration_D) body. Latent QRespiration_L=hwV(Wex−Win), V pulmonary ventilation rate, Wex ratio expiration air, Win inspiration (depends RHBuilding). QRespiration_D=cpV(Tex−Tin), cp specific dry constant pressure, Tex Tin respectively. = TBuilding.(3)Heat sweating (QSweat) QSweat=0.42(M−58.2), M metabolic rate.(4)Heat loss/gain radiation (Qr) clothed QRadiation=fefffclϵσ(Tcl4−Tmrt4), feff effective factor (view factor), fcl surface nude body, ϵ emissivity outer Tcl Tmrt mean radiant temperature.(5)Heat convection (Qc) QConvection=fclhc(Tcl−TBuilding), hc convective coefficient. Note dependent equating flow ambient. Assuming equilibrium, (Tsk), measured °C, by24Doherty T.J. Arens Evaluation physiological bases models.ASHRAE 1988; 94: 1371-1385Google ScholarTsk=35.7−0.0275M(Equation 1) conservation 2 neutrality equation:QMET−QSkin−QRespiration_L−QRespiration_D−QSweat−QRadiation−QConvection+QTMTL=0(Equation 2) QMET ( M) QTMTL It should noted original formulation, exist making equal 0 maintained adjusting RHBuilding (strategy practice). formulation Equation 2, floating parameters decided characteristics Furthermore, adding removing Addition treating main formulation. positive value heating), negative cooling). assumes complete balance. practices predicted vote (PMV) determines range met. defines PMV ranges -0.5 0.5. range, predicts When 0, met 2); values net (L) As result, incorporates byL=M−QSkin−QRespirationL−QRespirationD−QSweat−QRadiation−QConvection+QTMTL,(Equation 3) related L byPMV=TS×L(Equation 4) TS sensation Based data collected subjects, empirically as:TS=0.303×e(−0.036M)+0.028.(Equation 5) From Equations 4 5, −0.5 0.5 M, sets acceptable Consequently, 3. room), considered 0), necessary Alternatively, adjusted leaving constant; details iteratively Information. less stringent requirement compared equilibrium because < ensures comfortable, ensures15Van ∼95% chosen consistent existing standards. method, acknowledge debate comfort; therefore, warrants discussion. empirical relationship percentage dissatisfied students people sedentary activity,15Van whereas real involve larger diverse samples women were sensitive fluctuations optimum men. precise assessments, measurement rate (Equation depends fit data. recent paper, Kingma al.20Kingma concluded off 30% certain activities. questions applicable naturally ventilated buildings.25Rupp R.F. Kim Ghisi sensitivity typologies: Griffiths variable.Energy Build. 200: 11-20Crossref (30) Scholar,26Peeters Hensen D’haeseleer scales simulation.Appl. 86: 772-780Crossref According cannot without error buildings, partly adaptation indoor environment.15Van Therefore, proposed relates neutral indoors monthly outdoors.27de Brager G.S. Developing preference dear Brager.ASHRAE 1998; 104: 1Google Van Hoof15Van provided comprehensive controversy Fanger. PMV, if someone wanted remove empiricism concerns inherent methodology, derived principles any empiricism. worth noting unlike cold hot reservoirs, components, building’s design, since function characteristics. remember specified proper context United States Table 1; representative quietly seated summer (clo 0.5) winter 1.0). 55. Parameter 1 nominal values. performed study clo, met, velocity. chart