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Residential Renovation towards nearly zero energy CITIES

Energy demand and savings

Current state: total energy demand and demand uses distribution

Total energy demand for a building and for a dwelling has been estimated by means of Spanish national software tool “Calener”. It is result of the European Union Directive 2002/91/EC relating to the energy performance of buildings, as transposed into Spanish law by “RD.47/2007 The Energy Performance of Buildings (Certificates and Inspections)”.

Nowadays, Energy Performance Certificate is a measurement used in Spain only for certification of new planned homes, before they are built. But in order to have some initial data about current energy performance of the target district "Cuatro de Marzo", National Basic Procedure for energy certification has been applied. Specifically, energy consumption and the associated CO2 emissions has been estimated as the building type "Horizontal Block" were today planned to build.

About energy systems, in this district there is not any common heating system and neither a central heating installation in each building. Usually individual natural gas-fired boiler in each home is the energy production system, which produces hot water for the heater installation in the whole house, and also for the hot water net in kitchen and bathrooms. The most common heat distribution elements are radiators.

As consequence of the demand analysis, energy demand for a dwelling type „C‟ has been estimated in162,52 kWh/m2. Heating and Domestic hot Water are produced by natural gas. The other energy consumption in a dwelling is electrical consumption for appliances, lighting and cooling.

Planned energy efficiency measures and expected energy savings

The main objective of these refurbishment activities is the achievement of a comfort level, isolation level and installations functional level in the dwellings similar to new housing. The foreseen energy efficiency measures will be focused to reduce thermal consumption (insulation and shadings improvements and ICTs implementation), to reduce electrical consumption (occupancy sensor in common areas, more efficient lighting equipment and detailed billing), and also to reduce CO2 emissions by means of renewable energy systems as solar PV and solar thermal.

Energy renovation of a district in a city involves the carrying out of energy efficiency measures at different levels, from measures in the dwelling sphere, including buildings refurbishment and to district level. In this last one point, interaction between the different measures applied over buildings should be taken into account to put all together and also to draw new measures that in some way aim that final results will be more ambitious that the sum of the parts.

At building level, main planned measures are concerned to envelope improvement (passive measures),energy production systems (with special emphasis on renewable energies) and energy management systems. Each energy efficiency measure has a different effect in terms of energy savings or CO2 emissions reduction, that have been estimated taking into account the baseline data, the simulations and some special approach related with some existing studies.

Passive measures

First step in energy efficient renovation is always minimising demand. This fact supposes in the climate region of Valladolid, not only the reduction of heat demand in winters but also the reduction of cooling demand in summer. For these reasons improvements on insulation and inclusion of shading elements in buildings will be done.

  • Integral ventilated façade and roof renovation, improving the existing wall insulation and also improving glass window features will be carried out. Energy savings achieved by this measure have been estimated around the 30% of the total.
  • Shading elements will be installed in order to reduce in summer direct solar radiation, reducing cooling demand and therefore improving the comfort conditions. The shading elements consist on horizontal panels of 60 cm wide and situated at the high of the roof. They are designed to supply shadow over the windows in the building. In particular, windows facing to south and west should be protect from too much sun radiation in summer. Jointly to bioclimatic solutions like the use of plants and trees as humidity elements in summer, it is thought that no active systems will be needed in the future in the district.
  • Equipment efficiency improvements: regarding to electrical consumption, more efficient lighting (low consumption even LEDs bulbs) will replace old lighting systems, mainly in common areas but maybe into the dwellings too. Estimation of energy savings by this technological change is estimated in the 80% of the electrical consumption in lighting. That is around a third part of the electrical consumption.

Active measures

It will be raised three different solutions concerning active systems. Solar thermal facilities for domestic hot water, centralized biomass boiler, and solar photovoltaic panels.

  • With a solar thermal installation of around 12m2 per building and oriented to the south, it is expected to produce enough DHW to cover al least the 30% of the total demand and the estimated CO2 emissions avoided are almost 20 tons of CO2/yr.
  • Centralized biomass boiler as has been explained before, could be an efficient solution for the centralization of heat production in a quarter. This solution could be implemented in various configurations, for example, it is possible to install only one biomass boiler but also it is possible to install two boilers with half power each one in a cascade configuration, so that allows to switch only one of them when in mild cold seasons. Calculations show that a biomass boiler of 1000 Kwth covers the thermal needs for a group of 10 buildings of type1. It should be also considered the possibility of two boilers of 500 kWth. Estimated CO2 emissions avoided: 658 tons CO2/yr
  • It will take advantage of the good opportunities that solar energy in Spain can provide for electrical production. It is planned to install photovoltaics panels on the roof (in the free spaces of solar collectors) and also photovoltaic cells integrated over the new external facade.

ICTs based measures

Mainly energy management systems, will be installed.

  • Programmable thermostat. It is estimated by the International Energy Agency that energy savings that could be achieved by this measure are around a 10% of the total, only by means of the control of temperature, decreasing a par of degrees the temperature during the night.
  • Thermostatic valves on radiators are also a common and very profitable of energy efficiency measures that allows to save until the 20% of the energy used in a year for heating.
  • Occupancy sensor in common areas will be installed to avoid waste energy when it is not necessary

Consumption awareness: smart metering allows more detailed bill, and also real time consumption information. It was estimated in several studies that this kind of data allow save around 5% of the current energy consumed by a dwelling. Total amount of CO2 expected to avoid by ICTs based measures is estimated in 50 tons of CO2/yr.

Expected energy savings based on BEST tables calculation

Area of retrofi​tting:
81,000 m(only 21,000 have been considered to calculate scale of unit cost)

Total energy consumption before the renovation: 
174.54 kWh/m2yr

Total estimated energy consumption after the renovation:
56.03 kWh/m2yr

Total estimated energy saving:

Total avoided CO2 emissions without RES:
635 tons of CO2/yr

Total avoided CO2 emissions with RES:
894 tons of CO2/yr