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Energy retrofits in Hamburg

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A residential street in Karolinenviertel - typical of the buildings that benefit most from an energy retrofit

A residential street in Karolinenviertel – typical of the buildings that benefit most from an energy retrofit

Building a new, energy efficient building is relatively easy, and energy savings features such as added insulation or better windows are a small portion of the total building costs. It is a different story when retrofitting existing buildings, where costs may become prohibitive. Yet retrofitting existing buildings to minimize heating energy is a key part of climate change strategies for countries with cold climates, like Canada.

Germany has embarked on a fairly aggressive retrofit program of its own, with an objective of renovating one percent of the residential housing every year. But what is the best bang for the buck? In Hamburg, the planners of the building exposition IBA2013 tackled that question with four typical buildings: appartment buildings from the pre-war era, from the post-war reconstruction, and from the seventies, as well as a single-family house.

As may have been guessed, the pre-war low-rise appartments come out the clear winners, with the shortest pay-back period (14 years) and the biggest saving in terms of energy, about 330 kilowatt-hour per square meter of floor area every year. That’s a lot of carbon not emitted as a result. The calculations show show that these buildings, which comprise the bulk of the housing stock in Hamburg, should have priority. But all buildings considered show great potential for energy savings.

Regrettably, the authors focussed on the costs, but not on one intriguing aspect of housing retrofit programs: job creation. Sure, these programs have high up-front costs, but they should be considered investments in the future, as well as job creation mechanisms. Everywhere in the city, as I walk around, I see scaffoldings around buildings and trucks labelled “sanierung, renovierung, klimakontrolle”. I don’t know how many of these jobs are due to climate change intiatives, and how many are routine renovations; but one percent of the housing stock, whichever way you cut it, is a lot of jobs.

In this set of case studies, the renovations all consisted of improving the envelope performance by installing new windows, insulating walls, roof, and cellar ceiling to EnEV2009 standards, as well as replacing the natural gas boiler or furnace with a heat pump with ground sensors. Energy costs and amortization period were based on a cost of 0.07€/kWh for natural gas, and 0.18€/kWh for electricity. Though expected to increase, the energy costs were kept constant for the sake of calculating the amortisation, or pay-back, period.  These costs are high compared to BC, which has some of the lowest energy costs, undermining somewhat the case for retrofits; but the climate concern is the same everywhere.

The energy requirements in this comparison include only heating costs, no air-conditioning (very rare in residential Hamburg buildings), let alone the energy requirements of appliances. The heat loss that must be made up by heating is listed as “heating requirement”, while the actual cost of purchasing energy for heating is under the heading “total energy needs”. The units of energy needs are in kWh/m2a, that is, in kilowatt-hours per square meter of heated floor, per year. (A square meter is roughly equivalent to 10 squre feet.)

Before renovations, the total energy needed are greater than the heating requirements. That is because heating with natural gas is never 100% efficient, since some of the energy is lost up the chimney. Paradoxically, because heat pumps are used, the total energy needs are less than the energy needs after renovations. That is because heat pumps work much like refrigerators, except in reverse; this means that they consume only the electricity needed to pump the heat exchange fluid.

Case study 1
1920s appartment building, 5 floors, 15 units, 1349 m2 heated area, 5942 m3 heated volume
Heating requirements: 229 kWh/m2a before; 82 kWh/m2a after
Total energy needs: 360 kWh/m2a before; 31 kWh/m2after
Energy costs: 33,987 €/yr before; 7,552 €/yr after
Renovation costs: 273,800€ (envelope), 94,700€ (heat pump)
Amortisation period: 14 years

Case study 2
1950s single family bungalow, 1 floor, 1 unit, 101 m2 heated area, 380 m3 heated volume
Heating requirements: 183 kWh/m2a before; 52 kWh/m2a after
Total energy needs: 332 kWh/m2a before; 21 kWh/m2after
Energy costs: 2,346 €/yr before; 385 €/yr after
Renovation costs: 31,450€ (total)
Amortisation period: 31 years

Case study 3
1970s appartment building, 14 floors, 254 units, 18,012 m2 heated area, 68,360 m3 heated volume
Heating requirements: 69 kWh/m2a before; 36 kWh/m2a after
Total energy needs: 132 kWh/m2a before; 17 kWh/m2after
Energy costs: 169,570 €/yr before; 54,047 €/yr after
Renovation costs: 2,280,000€ (envelope), 257,000€ (heat pump)
Amortisation period: 22 years

Case study 4
1960s appartment building, 8 floors, 248 units, 3020 m2 heated area, 9805 m3 heated volume
Heating requirements: 155 kWh/m2a before; 47 kWh/m2a after
Total energy needs: 250 kWh/m2a before; 19 kWh/m2after
Energy costs: 52,888 €/yr before; 10,366 €/yr after
Renovation costs: 654,500€ (envelope), 98,500€ (heat pump)
Amortisation period: 18 years

Source: Hellweg, Uli, ed, 2010. Energy Atlas: Future Concept Renewable Wilhelmsburg. Berlin: Jovis Verlag.

 

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Written by enviropaul

December 8, 2015 at 11:23 am

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