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More and more ener­gy for cooling

Due to the cli­mate-induced rise in tem­per­a­ture, the cool­ing require­ments of build­ings will con­tin­ue to increase. An extrap­o­la­tion by Empa researchers based on data from the NEST build­ing and future cli­mate sce­nar­ios for Switzer­land shows that this increase in ener­gy demand for cool­ing is like­ly to be sub­stan­tial and could have a strong impact on our future — elec­tri­fied — ener­gy system.

Due to cli­mate change, the aver­age tem­per­a­ture will rise in the com­ing decades. This should also lead to a sig­nif­i­cant increase in the num­ber of so-called cool­ing degree days. These mea­sure the num­ber of hours that the ambi­ent tem­per­a­ture is above a thresh­old at which a build­ing needs to be cooled to keep the indoor tem­per­a­ture at a com­fort­able lev­el. The ris­ing val­ues may lead to an increase in the instal­la­tion of cool­ing appli­ances in pri­vate house­holds. This could fur­ther increase the ener­gy demand for cool­ing build­ings, which is already set to increase due to cli­mate change and pop­u­la­tion growth.

Head-to-head race between heat­ing and cooling

In order to gain a bet­ter under­stand­ing of how large this increase will be in Switzer­land, Empa researchers have analysed the heat­ing and cool­ing require­ments of the NEST research and inno­va­tion build­ing. “Tak­ing into account the ambi­ent tem­per­a­tures, we were able to extrap­o­late the future ther­mal ener­gy demand of build­ings based on the cli­mate sce­nar­ios for Switzer­land. In addi­tion to cli­mate change, we also took pop­u­la­tion growth and the increas­ing use of cool­ing devices into account,” explains Robin Mutschler, post­doc at Empa’s Urban Ener­gy Sys­tems Lab.

The results fore­cast a sharp increase in cool­ing ener­gy demand: Assum­ing an extreme sce­nario in which the whole of Switzer­land would be depen­dent on air con­di­tion­ing, almost as much ener­gy would be need­ed for cool­ing as for heat­ing by the mid­dle of the cen­tu­ry. Expressed in fig­ures, this cor­re­sponds to about 20 ter­awatt hours (TWh) per year for heat­ing and 17.5 TWh for cool­ing. The required cool­ing ener­gy was cal­cu­lat­ed inde­pen­dent­ly of the tech­nol­o­gy: If this is pro­vid­ed by revers­ing a heat pump process, e.g. with COP 3 for cool­ing, the elec­tric­i­ty demand for 17.5 TWh of cool­ing ener­gy amounts to about 5.8 TWh.

The heat­ing require­ments of the occu­pied mod­ules in the NEST build­ing are com­pa­ra­ble to those of a mod­ern apart­ment build­ing. The cal­cu­lat­ed fig­ures are there­fore rep­re­sen­ta­tive if it is assumed that the aver­age Swiss build­ing stock cor­re­sponds to the NEST build­ing. When this will be the case depends on the ren­o­va­tion rate. Even in a more mod­er­ate sce­nario, cool­ing demand in Switzer­land will increase sig­nif­i­cant­ly. In this sce­nario, the researchers assume an addi­tion­al ener­gy demand of 5 TWh per year.

Strong influ­ence on the Swiss ener­gy system

The ener­gy demand of Swiss build­ings today accounts for around 40 per­cent of the total ener­gy demand. The main part of this is account­ed for by heat­ing. This is like­ly to remain the case until at least the mid­dle of the 21st cen­tu­ry, but ener­gy demand for cool­ing build­ings is expect­ed to increase sharply. If ther­mal ener­gy is pro­vid­ed by heat pumps, which can also cool, this poten­tial­ly has a strong impact on the over­all ener­gy sys­tem and in par­tic­u­lar on elec­tric­i­ty as an ener­gy carrier.

At present, only a small pro­por­tion of Swiss house­holds are thought to have air con­di­tion­ing, but the num­ber of house­holds with heat pumps is increas­ing. The Empa researchers esti­mate that the num­ber of house­holds with cool­ing appli­ances could rise to over 50 per­cent due to the increase in cool­ing degree days. This increase could lead to sig­nif­i­cant peaks in demand on hot days. An addi­tion­al ener­gy demand of 5 TWh for cool­ing would cor­re­spond to about 2 per­cent of today’s elec­tric­i­ty demand if cool­ing is done with heat pumps. In an extreme sce­nario, the demand for cool­ing could even reach 10 per­cent of today’s total elec­tric­i­ty demand. How­ev­er, this will not be even­ly dis­trib­uted through­out the year, but will cor­re­late with hot peri­ods, which may lead to peaks in demand. It is advan­ta­geous that the cool­ing require­ment is rel­a­tive­ly well cov­ered by the elec­tric­i­ty gen­er­at­ed by pho­to­volta­ic sys­tems. The impact of cool­ing res­i­den­tial build­ings will be sig­nif­i­cant­ly high­er com­pared to office build­ings, as they account for about two thirds of the build­ing area.

Based on these find­ings, it is clear to the researchers that these devel­op­ments should be tak­en into account when con­struct­ing new build­ings and that the pos­si­bil­i­ties, such as pas­sive cool­ing, should be ful­ly exploit­ed. “Build­ing archi­tec­ture should no longer focus only on opti­miz­ing heat loss­es in win­ter, but also on reduc­ing heat gains in sum­mer,” Mutschler says. This could be achieved, for exam­ple, through urban plan­ning mea­sures for cli­mate adap­ta­tion at neigh­bour­hood lev­el, the imple­men­ta­tion of heat reduc­tion pro­grammes or the reduc­tion of the pro­por­tion of glaz­ing in build­ings. “In addi­tion, it is cen­tral that pol­i­cy­mak­ers also address this devel­op­ment and inves­ti­gate how best to meet the increas­ing demand for cool­ing ener­gy while min­i­miz­ing the impact on the future decar­bonized ener­gy sys­tem,” Mutschler said. A pos­si­ble con­tri­bu­tion to the cool­ing of build­ings can be pro­vid­ed by dis­trict cool­ing sys­tems, which have already been suc­cess­ful­ly imple­ment­ed in Switzer­land — for exam­ple in Gene­va. Oth­ers are in the mak­ing, for exam­ple in Zug.