Energy performance of buildings Energy in building

Energy performance of buildings Basic aims of EPB evaluation: energy need for heating total energy use primary energy use classification of low-E houses Energy performance certificate classification of energy passive houses, EP certificate Calculation methods: set of EN ISO (basic EN ISO 13790), national directives…

Definitions Energy need for heating [GJ, MWh, kWh/m2] Heat needed to maintain the required internal design temperature θi in a space during a certain period (usually a year). Theoretical value for 100 % efficiency of heating system. Energy use for heating [GJ, MWh, kWh/m2] Total amount of energy necessary to cover the energy need for heating QH,nd by means of real heat sources. It takes into account standardized efficiencies of heat sources, heat distribution and heat emission.

Definitions Total energy use [GJ, MWh, kWh/m2] Primary energy It can be different from measured values (many inputs must be guessed for the calculation…) Total amount of energy delivered to a building during a certain period (usually 1 year). It takes into account standardized efficiences of HVAC and standardized usage of building (e.g. from the point of view of lighting and hot water use). Primary energy Energy from nature, which was not transformed in some facility. Primary energy use [GJ, MWh, kWh/m2] Amount of primary energy necessary to cover total delivery of energy to building Quse during certain period (usually 1 year). It is derived by means of converse factors from Quse according to type of energy carrier (see following). It show environmental impacts of the building.

Energy performance of buildings Calculation methods: - (seasonal – over heating period – only exceptionally) - monthly – present-day standard - hourly – dynamic simulation programs for complicated buildings Climate data: for specific location (for alayses of real energy performance) reference data (for energy certificate, calculations for various grant programs) Input data preparation: definition of zones and their properties (volume, floor area) areas and properties of constructions (U, g …) properties of thermal joints properties of technical systems (HVAC) selection of appropriate calculation tool

Energy need for heating Energy performance of buildings Energy need for heating

Energy need for heating Aim of calculation: classification of buildings: under 50 kWh/m2: low-energy buildings under 15 kWh/m2: passive buildings more subtle limits in TNI 730329 and 730330 to get a value without influence of HVAC (grant applications) Factors taken into account in calculation: heat losses through constructions and their joints heat gains (internal + solar) ability of constructions to accumulate heat ventilation mode (natural, forced, heat recovery) intermittent heating and variable usage, if it is acceptable for given purpose of calculation

Energy need for heating [MWh] or [GJ] for each month, annual need = sum of positive values Basic formula from EN ISO 13790: energy need necessary to cover heat loss of building the same formulas as for the calculation of Uem Exception: heat transfer via the ground, it consists of steady-state and periodic part, various for individual months, calculation according to EN ISO 13370. Approximate calculation:

Energy need for heating Basic formula from EN ISO 13790: energy need necessary to cover heat loss of building [MWh] or [GJ] for calculations: 0,5 / h ventilation heat transfer coefficient natural ventilation forced ventilation (+ heat recovery)

Energy need for heating Basic formula: energy need necessary to cover heat loss of building [MWh] or [GJ] required set-point internal temperature during calculated period duration of calculated period mean external air temperature during calculated period

generally time-dependent, values, typically in W/m2 Energy need for heating Basic formula: [MWh] or [GJ] Solar gains QH,s: windows solar elements (TIM, Trombe walls, sunspaces) (opaque constructions) + Internal gains QH,i: persons lighting appliances generally time-dependent, usually taken as mean values, typically in W/m2 (e.g. family house: 2-6 W/m2)

Energy need for heating Basic formula: [MWh] or [GJ] Praha horizon Total energy of Sun irradiation during 1 month falling on 1 m2 (depending on orientation) Solar gains QH,s: windows solar elements (TIM, Trombe walls, sunspaces) (opaque constructions)

Energy need for heating shading factor for overhangs shading factor for side fins shading factor for other buildings etc. Basic formula: [MWh] or [GJ] default values in EN 13790 effective collecting area (each window separately): Solar gains QH,s: windows solar elements (TIM, Trombe walls, sunspaces) (opaque constructions) window area shading reduction factor reduction factor for moveable shading frame reduction factor (ratio of frame area to total window area)

Energy need for heating Basic formula: [MWh] or [GJ] total solar energy transmittance of glazing effective collecting area (each window separately): Solární zisky QH,s: okna solární prvky (TIM, Trombeho stěny, zimní zahrady) (neprůsvitné kce) It expresses total solar energy entering interior: window area shading reduction factor direct transmission of energy reflection reduction factor for moveable shading secondary radiation secondary radiation absorption declared by producer (for perpendicular radiation), for calculation: 90% from g┴

Energy need for heating Basic formula: [MWh] or [GJ] Gain utilization factor: gains cannot be always totally utilized utilization depends on internal heat capacity C … and on ratio between gains and losses calculation acc. to EN ISO 13790 simplified model more exactly for hourly method

Energy need for heating Specific energy need for heating: [kWh/m2] Total floor area: only from heated or cooled zones (without garages etc.!) includes all floors in heated zones usually calculated from external dimensions

Energy use and primary energy Energy performance of buildings Energy use and primary energy

Total energy use Aim of calculation: evaluation of total energy use in building (usually in kWh/m2) energy performance certificates What is taken into account: efficiencies of HVAC systems (production, distribution + emission) all energy flows in building and of course: properties of constr., th. joints, gains… distribution (pipes) source (boiler) emission (radiators)

Total energy use Basic components of energy balance: [MWh] or [GJ] energy use for heating energy use for cooling energy use for mech. ventilation energy use for relative humidity adjustment energy use for hot water preparation energy use for lighting (event. also for appliances) Energy uses include also relevant auxiliary energy uses (pumps, ventilators…) calculation for each month, annual use = sum of monthly values

Total energy use Annual energy use: Monthly energy uses:

Total energy use Principle of calculation of partial energy use for heating : heat source efficiency heat distribution efficiency heat emission efficiency auxiliary energy use (pumps, regulation…) part of energy from solar collectors used for heating Actually much more complicated!

Total energy use Principle of calculation of partial energy use for cooling: - at first, energy need for cooling (analogy to heating: gains, losses + utilization) - further on, all efficiencies and auxiliary energies are taken into account Principle of calculation of partial energy use for HW preparation: - starting point: presumed annual (monthly) HW use, starting and final temperature of water - further on, all efficiencies and auxiliary energies are taken into account Principle of calculation of partial energy use for lighting: - starting point: presumed el.power input + light sources efficiencies - (the same for appliances) IMPORTANT: Average energy behaviour of building is evaluated in monthly method, therefore all efficiencies are also mean values! Principle of calculation of partial energy production: - starting point: properties of PV panels and cogeneration units

Total energy use Specific energy use of the building: [kWh/m2] Total floor area: - only from heated or cooled zones (without garages etc.!) - includes all floors in heated zones - usually calculated from external dimensions

Non-renewable primary energy ratio energy transformation factor calculation by energy carriers CO2 emissions: analogy emission factor in kg/kWh for individual energy carriers

Precision of calculation dependent on the aim of calculation for common situations and buildings, the precision of monthly calculation: is sufficient for annual sum shows sometimes errors in some months (spring, autumn) monthly calculation is not sufficient for complicated buildings – dynamic simulations are necessary (ESP-r, TRNSYS etc.) comparison with the reality: problematic (how to create the reality model?) step-by-step calibration of the model can be done

Default input values air change rate: natural: n = 0,5 h-1 forced: 25 – 30 m3/(h.prs) [offices 50 m3/(h.prs)] heat recovery efficiency for ventilation: 75 – 80 % modern heating system efficiency: 80 – 95 % internal gains - family and residential houses: ~ 2 – 6 W/m2 gains must be reduced according to presumed building usage (8 h during 5 days in a week etc.) the same can be done also for air change rate and required internal design temperature