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Energy in Buildings Prof. Tânia Sousa

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1 Energy in Buildings Prof. Tânia Sousa taniasousa@ist.utl.pt
Gestão de energia: 2012/2013 Energy in Buildings Prof. Tânia Sousa

2 Energy Consumption in Buildings
Buildings account for 40% of total energy consumption in the European union What about Portugal? In 2010 the final consumption of services + domestic sector represented 55% of the final energy consumption Do you think that the fraction of primary energy would be higher or lower? Why?

3 Energy Consumption in Buildings
Most effective strategy to reduce energy use in buildings (Harvey, 2010): Reduce heating and cooling loads through a high-performance envelope high degree of insulation, windows with low U values in cold climates and low solar heat gain in hot climates, external shading and low air leakage Meet the reduced load as much as possible using passive solar heating, ventilation and cooling techniques while optimizing the use of daylight Use the most efficient mechanical equipment to meet the remaining loads Ensure that individual energy-using devices are as efficient as possible and properly sized

4 Energy Consumption in Buildings
How much energy reduction can we achieve? Passive house standard: heating  15kWh/m2 per year cooling  15 kWh/m2 per year TPE  120 kWh/m2 per year n50 ≤ 0.6 / hour From 220 kWh/m2/year to kWh/m2/year Triple-glazed windows with internal venetian blinds & mechanical ventilation with 82% heat recovery

5 Energy Consumption in Buildings
How much does it cost?

6 Buildings – High Performance Envelope
The effectiveness of the thermal envelope depends of insulation levels in the walls, ceiling and basement Insulation levels control the heat flow by conduction & convection through the exterior and the interior U value (W/m2/K), the heat trasnfer coefficient, is equal to the heat flow per unit area and per degree of inside to outside temperature difference The U value of a layer of insulation depends on its length and type of material

7 Buildings – High Performance Envelope
The effectiveness of the thermal envelope depends of insulation levels in the walls, ceiling and basement The most highly insulated houses have U= W/m2/K Blown-in cellulose insulation (fills the gaps) Foam insulation Vaccum insulation panels

8 Buildings – High Performance Envelope
The effectiveness of the thermal envelope depends on the insulation levels of windows Windows offer substantially less resistance to the loss of heat than insulated walls Single glazed windows have a typical U-value of 5W/m2/K which can be reduced to to 2.5 and 1.65W/m2/K with double and triple glazing because of the additional layers of air The U-value of 2.5W/m2/K of double glazed windows can be reduced to 2.4W/m2/K and 2.3W/m2/K with Argon and krypton Double and triple glazing vaccum windows can reduce the U value to 1.2 and 0.2W/m2/K

9 Buildings – High Performance Envelope
The effectiveness of the thermal envelope depends on the gain/loss energy by radiation Windows permit solar energy to enter and loss of infrared radiation Low emissivity coatings reflect more (reduce SHGC), i.e., reduce heat gains in summer and winter Low emissivity coatings can reduce loss of heat by infrared radiation The solar heat gain coefficient, SHGC, is the fraction of solar radiation inicident on a window that passes through the window

10 Buildings – High Performance Envelope
The effectiveness of the thermal envelope depends on the air leakage The net heat flow due to an air exchange at rate r is: The stack effect promotes air leakage Cold air is sucked into the lower part and warm air exits through the upper part through craks and openings because it is lighter. Stack effect can account for up to 40% of heating requirements on cold climates The wind effect

11 Buildings – High Performance Envelope
The effectiveness of the thermal envelope depends on the air leakage Careful application of a continuous air barrier can reduces rates of air leakage by a factor of 5 to 10 compared to standard practice (enforcement of careful workmanship during construction) Buildings with very low air leakage require mechanical ventilation (95% of the available heat in the warm exhaust air can be transfered to the incoming cold air) to keep indoor air quality

12 Energy Balance in Open Systems
Heat Exchangers: Used in power plants, air conditioners, fridges, liquefication of natural gas, etc Transfer energy between fluids at different temperatures Nos três acetatos seguintes coloquei bonecos para poderes explicar melhor as leis da ternodinâmica Direct Contact Heat Exchanger Counter-flow Heat exchanger Direct Flow Heat Exchanger

13 Buildings – The role of shape, form, orientation and glazed %
Building shape & form Have significant impacts on heating and cooling loads and daylight because of the relation between surface area and volume Which one minimizes heat transfer by conduction and convection? Building orientation For rectangular buildings the optimal orientation is with the long axis facing south Why?

14 Buildings – The role of shape, form, orientation and glazed %
Glazing fractions High glazing fractions increase energy requirements for heating and cooling There is little additional daylighting benefit once the glazed fraction increases beyond 30-50% of the total façade area House size The living area per family member increased by a factor of 3 between and 2000 in the US

15 Buildings – (almost) Passive solar heating, ventilation & cooling
Evaporative Cooling:

16 Buildings – Passive (almost) solar heating, ventilation & cooling
Thermal induced ventilation & cooling: Earth Pipe cooling Large Atria

17 Buildings – Passive (almost) solar heating, ventilation & cooling
Wind induced ventilation & cooling: Wind catcher

18 Buildings – Passive (almost) solar heating, ventilation & cooling
Passive Solar Heating & Lighting Shading Light tubes Light shelves

19 Buildings: Mechanical Equipment
In evaluating the energy efficiency of Mechanical Equipment the overall efficiency from primary to useful energy should be taken into account This is particularly important in the case of using Mechanical Equipments that use electricity (produced from fossil fuels)

20 Buildings: Mechanical Equipment for heating
Furnaces heat air and distribute the heated air through the house using ducts; are electric, gas-fired (including propane or natural gas), or oil-fired. Efficiencies range from 60 to 92% (highest for condensing furnaces) Boilers heat water, and provide either hot water or steam for heating; heat is produced from the combustion of such fuels as natural gas, fuel oil, coal or pellets. Efficiencies range from 75% to 95% (highest for condensing boilers)

21 Buildings: Mechanical Equipment for heating & cooling
Electrical-resistance heating Overall efficiency can be quite low (primary -> useful) Heat-Pumps Overall efficiency can be quite good It decreases with T Air-source and ground-source For cooling & heating District Heating/Colling For heating & cooling Users don’t need mechanical equipment

22 Buildings: Mechanical Equipment for cooling
Chillers Produce cold water which is circulated through the building Electric Chillers: use electricity Absorption chillers: use heat (can be waste heat from cogeneration) Electric chillers, COP = (larger units have a higher COP) Absorption chillers, COP =

23 Buildings: HVAC Systems
Ventilate and heat or cool big buildings All air systems: air at a sufficient low (high) T and in sufficient volumes is circulated through the building to remove (add) heat loads CAV: constant air volumes VAV: variable air volumes Air that is circulated in the supply ducts may be taken entirely from the outside and exhausted to the outside by the return ducts or a portion of the return air may be mixed with fresh air Incoming air needs to be cooled and dehumidified in summer and heated and (sometimes) humidified in winter Restrict air flow to ventilation needs and use additional systems for additional heating/cooling Heat exchangers that transfer heat between outgoing and incoming air flows

24 Buildings: Mechanical Equipment for water heating
Electrical and natural gas heaters Efficiency of natural gas heaters is 76-85% Efficiency of oil heaters is 75-83% There is heat loss from storage tanks Point-of-use tankless heaters have losses associated with the pilot light There are systems that recover heat from the warm wastewater with % efficiencies

25 European Directives European Directives on the Energy Performance of Buildings Directive 2002/91/EC of the European Parliament and Council (on the energy performance of buildings): This is implemented by the Portuguese Legislation RCCTE and RCESE Directive 2010/31/EU of the European Parliament and Council (on the energy performance of buildings)

26 Directive 2010/31/EU: Aims Reduction of energy consumption
Use of energy from renewable sources Reduce greenhouse gas emissions Reduce energy dependence Promote security of energy supplies Promote technological developments Create opportunities for employment & regional development Links with aims of SGCIE?

27 Directive 2010/31/EU: Principles
The establishment of a common methodology to compute Energy Performace including thermal characteristics, heating and air conditioning instalations, renewable energies, passive heating and cooling, shading, natural light and design

28 Directive 2010/31/EU: Principles
Set Minimum Energy Performance Requirements Requirements should take into account climatic and local conditions and cost-effectiveness

29 Directive 2010/31/EU: Principles
Energy Performance Requirements should be applied to new buildings & buildings going through major renovations

30 Directive 2010/31/EU: Principles
Set System Requirements for: energy performance, appropriate dimensioning, control and adjustment for Technical Building Systems in existing and new buiildings

31 Directive 2010/31/EU: Principles
Increase the number of nearly zero energy buildings

32 Directive 2010/31/EU: Principles
Establish a system of Energy performace certificates. Energy Performance certificates must be issued for constructed, sold or rented to new tenants Buildings occupied by public authorities should set na example (ECO.AP in 300 public buildings in Portugal)

33 Directive 2010/31/EU: Principles
Regular maintenance of air conditioning and heating systems Independent experts

34 Implementation of the directives
Directive 2002/91/EC was implemented with: Directive 2010/31/EU was not yet implemented DL 78/2006, the National Energy Certification and Indoor Air Quality in Buildings (SCE). DL 79/2006, Regulation of HVAC Systems of Buildings (RSECE). DL 80/2006, Regulation of the Characteristics of Thermal Performance of Buildings (RCCTE).

35 RCCTE - Aims General aims: Specific Aims: RCCTE – Aim
Methodology for computing energy performace of buildings Set minimum energy performance standards Implement Energy Certification of buildings Specific Aims: Limitation of annual energy needs for heating, cooling, domestic hot water and primary energy Limitation of heat transfer coefficients Limiting of solar factors Installation of solar panels 35

36 RCCTE – Domain of Application
Buildings that RCCTE applies to: Residential Comercial Small Big Pnom < 25 kW Pnom > 25 kW New RCCTE Old Major Renovation No Renovation 36

37 RCCTE – Indoor & Outdoor Conditions
RCCTE - Outdoor conditions Reference Indoor conditions 20ºC in heating season 25ºC and 50% relative humidity in the cooling season Consumption of 40 liters of water at 60ºC/occupant . day Reference Outdoor conditions: Portugal is divided in winter and summer climatic zones 37

38 RCCTE – Outdoor Conditions
Reference Outdoor conditions: 38

39 RCCTE – Outdoor Conditions
Climate RCCTE – Outdoor Conditions Heating Degree-days are: Where: Tb is the desired indoor temperature (20ºC) Tj is the temperature outside the hours j The Degree-days are calculated for an entire year For example, to Lisbon, for Tb = 20 º C, heating degree days are 1190 º C.day. Knowing the heating season is 6 months (180 days), the average daily GD (GDI) will be 6.6 º C. 39

40 Heating Degree Days – a comparison

41 RCCTE – Outdoor Conditions
Climate RCCTE – Outdoor Conditions Outdoor project temperature The outside project temperature is calculated on a cumulative probability of occurrence of 99%, 97.5%, 95% and 90%. A cumulative probability of occurrence of 99% means that in summer the temperature indicated is exceeded only in probabilistic terms, 1% of the time, ie, 30 hours per year (e.g. Lisbon). 41

42 RCCTE – Fundamental thermal Indices
RCCTE – Indices e parameters The thermal behavior of buildings is characterized using the following fundamental thermal indices: Nic Nominal Annual Needs of Useful Energy for Heating Ni The corresponding maximum permissible Nic ≤ Ni Nvc Nominal Annual Needs of Useful Energy for Cooling Nv The corresponding maximum permissible Nvc ≤ Nv Nac Nominal Annual Energy needs for Domestic Hot Water Na The corresponding maximum permissible Nac ≤ Na Ntc Nominal Annual Energy needs for Primary Energy Nt The corresponding maximum permissible Ntc ≤ Nt 42

43 RCCTE – Additional parameters
RCCTE – Indices e parameters The thermal behavior of buildings is characterized using the parameters: more demanding for harsher winters more demanding for harsher summers Additional parameters U Heat transfer coefficients of walls Umax The corresponding maximum permissible Heat Transfer Coefficients of Thermal Bridges 2 x Umax Solar factor of fenestration (for windows not facing NE-NW with area > 5%) Fs Fsmax The corresponding maximum permissible 43

44 RCCTE – Fundamental thermal Indices: Heating
Heating: Maximum Allowable Needs (Ni) [kWh / (m2.year)] FF ≤ 0.5 :: Ni = 4,5 + 0,0395 GD 0,5 < FF ≤ 1 :: Ni = 4,5 + (0,021+ 0,037FF) GD 1 < FF ≤ 1,5 :: Ni = [4,5 +(0,021+ 0,037FF) GD] (1,2 – 0,2 FF) FF > 1,5 :: Ni = 4,05 + 0,06885 GD Form factor: FF = ( (Aext) +  ( Aint))/V GD :: Degree day (ºC * day) more demanding for smaller FF Nic < Ni Heating: Nominal Needs (Nic) [kWh / (m2.year)] Nic = (Qt + Qv – Qgu) / Ap Qt = x GD x  (A x U) Qv = 0,024 (0,34 x R x Ap x Pd) x GD to keep the Tint = 20ºC during the heating season Qt: heat loss by conduction & convection through the surrounding Qv: heat losses resulting from air exchange Qgu: solar gain and internal load 44

45 Current average residential heating energy use (Harvey, 2010)
kWh/m2/yr for new residential buildings in Switzerland and Germany 220 kWh/m2/yr average of existing buildings in Germany kWh/m2/yr for existing buildings in central and eastern Europe For Lisbon the maximum heating allowable needs are: Passive house standard: 15 kWh/m2/yr

46 RCCTE – Fundamental thermal Indices: Cooling
Cooling: Maximum Allowable Needs (Nv) [kWh/(m2.year)] V1 (North) : Nv = 16 V1 (South) : Nv = 22 V2 (North) : Nv = 18 V2 (South) : Nv = 32 V3 (North) : Nv = 26 V3 (South) : Nv = 32 Açores : Nv = 21 Madeira : Nv = 23 Cooling: Nominal Needs (Nvc) [kWh / (m2.year)] Nvc = Qg * (1 - ) / Ap (kWh/m2year) Qg : Total gross load (internal + walls + solar + air renewal)  : Load Factor Nvc < Nv to keep the Tint = 25ºC during the cooling season 46

47 RCCTE – Fundamental thermal Indices: Hot Water
Domestic Hot Water Domestic Hot Water: Maximum Allowable Needs (Na) [kWh / (m2.year)] Na = 0,081 MAQS nd/Ap MAQS : Reference consumption (40 liters per occupant) nd : Reference n. of days with DHW (residential:365) N. of occupants: T0=2; TN=n+1 1 m2 solar panel collector per occupant or 50% of available area if solar exposition is adequate Domestic Hot Water: Nominal Needs (Nac) [kWh / (m2.year)] Nac = (Qa/ηa – Esolar – Eren)/Ap Qa: Conventional useful energy requirements ηa: Efficiency of the conventional systems ESolar: Contribution of solar thermal panels for DHW Eren: Contribution to other renewable for DHW Qa : (MAQS * 4187 * T * nd) / ( ) (kWh/year) Maqs = 40 l /occupant . Day*nº occupants T : 45º (15ºc  60ºc) Nac < Na 47

48 RCCTE – Fundamental thermal Indices: Primary Energy
Primary energy: Maximum Allowable Needs (Nt) [kgep/(m2.year)] Nt = 0,9 (0,01Ni + 0,01 Nv + 0,15 Na) Primary energy : Nominal Needs (Ntc) [kgep/(m2.year)] Ntc = 0,1 (Nic/ηi)Fpui + 0,1 (Nvc/ηv)Fpuv + Nac Fpua Fpu : Conversion factor from final energy to primary energy Electricity: Fpu = kgep / kWh Fuels: Fpu = kgep / kWh In the absence of more precise data consider, eg: Electrical resistance = 1 Boiler fuel gas = 0.87 Heat Pump = 3 (cooling) and 4 (heating) Ntc < Nt 48

49 Energy Performance Certificate
Energy label Energy Performance Certificate Energy Labelling: R = Ntc / Nt R A A+ New buildings (licensed after 2006) B B 1 C D 2 E Old buildings F 3 G 49

50 RCESE - Aims General aims: Specific Aims: RCCTE – Aim
Methodology for computing energy performace of buildings Set minimum energy performance standards Implement Energy Certification of buildings Regular inspection of boilers and air conditioning in buildings Specific Aims: Limitation of annual energy needs for heating, cooling, and primary energy Limitation of heat transfer coefficients Limiting of solar factors Maintenance of HVAC systems Monitoring and energy audits 50

51 RCESE – Domain of Application
Structure Buildings that RCESE applies to: Residential Comercial Small Big Pnom < 25 kW Pnom > 25 kW New RCCTE RSECE   RSECE   RSECE   RSECE   Old Major Renovation   RSECE   RSECE No Renovation 51

52 RCESE – Indoor & Outdoor Conditions
RSECE - Outdoor conditions Indoor conditions the same of RCCTE air velocity can not exceed 0,2 m/s QAI (minimum air renovation and maximum concentration of air polutants) Reference Outdoor conditions: Portugal is divided in winter and summer climatic zones 52

53 RCESE - IEE IEE Methodology to compute Energy Performance
IEE : Energy Efficiency Indicator (kgep/(m2.year)] This value must be less than the tabled IEE to the proposed activity IEE = IEEi + IEEv + Qout/Ap Heating Other consumptions Cooling IEEi = (Qaq / Ap) x Fci Qaq : primary energy consumption for heating (kgep/year) IEEv = (Qarr / Ap) x Fcv Qarr : primary energy consumption for cooling (kgep/year) Fci : Correction factor for heating, Fci = Ni1/Nii Fcv : Correction factor for cooling, Fcv = Nv1/Nvi Renewable energies are not included Real energy consumptions (old) or simulation (new) 53

54 Correction Factors

55 RCESE – Fundamental thermal Indices: Heating & Cooling
Heating: Maximum Allowable Needs (Ni) [kWh / (m2.year)] FF ≤ 0.5 :: Ni = 4,5 + 0,0395 GD 0,5 < FF ≤ 1 :: Ni = 4,5 + (0,021+ 0,037FF) GD 1 < FF ≤ 1,5 :: Ni = [4,5 +(0,021+ 0,037FF) GD] (1,2 – 0,2 FF) FF > 1,5 :: Ni = 4,05 + 0,06885 GD Form factor: FF = ( (Aext) +  ( Aint))/V GD :: Degree day (ºC * day) GD=1000 degree days Cooling: Maximum Allowable Needs (Nv) [kWh/(m2.year)] V1 (North) : Nv = 16 V1 (South) : Nv = 22 V2 (North) : Nv = 18 V2 (South) : Nv = 32 V3 (North) : Nv = 26 V3 (South) : Nv = 32 Açores : Nv = 21 Madeira : Nv = 23 55

56 RCESE – Minimum Energy Performance
Structure Minimum Energy Performance Requirements: If the minimum energy performance requirements of old big comercial buildings are not met than there is na energy audit to develop an energy rationalization plan and all efficiency measures with economic viability have to be implemented Residential Comercial Small Big Pnom < 25 kW Pnom > 25 kW New RCCTE Nic ≤ 80%Ni,RCCTE Nvc ≤ 80%Nv,RCCTE IEE ≤ IEEmax Old Major Renovation No Renovation 56

57 IEE tabled values for existing buildings

58 IEE tabled values for new buildings or major renovations
58

59 Energy Performance Indicator
Energy label Energy Labeling: Depends on IEEnom, on IEEREF and on the S parameter 59

60 Energy Performance Indicator
Energy label Energy Performance Indicator Energy Labeling: Old buildings New buildings (licensed > 2006) IEE (kgep/year. m2) S IEEref S A+ A B B- C D E F G 60

61 System Requirements for HVAC
Limit the installed power: Heating or cooling Pnom < 1.4 of the power needed Promote Energy Efficiency If Pnom> 100 kW than HVAC system with centralized heat production The connection to centralized heating and cooling systems (if available) is mandatory The heating power obtained by Joule effect cannot exceed 5% of the heating thermal power Control and regulation systems Control confort temperatures Turn off when the space is not used Monitoring (Pnom> 100 kW ) and Energy Management Systems (Pnom> 200 kW ) with centralized optimization (Pnom> 250 kW ) Audits to big boilers and AC

62 Differences between Directives 2002/91/EC and 2010/31/EU
2010/31/EU has requirements on increasing the number of nearly zero-energy buildings; 2010/31/EU has requirements on the minimum energy performance of all (not only on big) existing buildings subject to major renovations In 2010/31/EU the framework for energy performance: Based on the computed or actual annual energy consumed in order to meet different needs associated with typical behavior Energy performance indicator and a numerical indicator of primary energy consumption

63 Differences between Directives 2002/91/EC and 2010/31/EU
2010/31/EU sets the minimum energy performance requirements targeting cost-optimal levels (to be calculated in accordance with a comparative methodology framework). 2010/31/EU considers that the methodology for the identification of cost-optimal levels should : take into account use patterns, outdoor climate conditions, investment costs and maintenance and operating costs; be computed for reference buildings with different functionalities and geographic locations; define the efficiency measures that should be assessed; consider the expected economic life-cycle of the building;

64 Differences between Directives 2002/91/EC and 2010/31/EU
2010/31/EU considers that the technical, environmental and economic feasibility of high-efficiency alternative systems such as (decentralized energy supply systems based on energy from renewable sources, cogeneration, district or block heating or cooling, heat pumps) should be considered for all (not only > 1000 m2) new buildings 2010/31/EU considers that when all buildings (not only > 1000 m2) undergo major renovation, the energy performance of the building or the renovated part thereof is upgraded in order to meet minimum energy performance requirements


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