House - Energy Exercise

Fausto Simões - Janeiro 2007 Email:
Some cost-effective measures can better the energy performance of our homes. You can have comfortable houses, even more comfortable houses, lower energy bills, a more even and lower demand to the energy plants and less pollution. The residential sector represents the main contributor to CO2 emissions from the EU building stock as it accounts for 77% of all emissions (

This exercise lets you explore the impact of some of those measures on your annual utility bills, energy consumption and related CO2 emission. The calculations can be performed for 4 different Portuguese and other 4 U.S. cities representing a range of climates.

You can modify your building or you appliance efficiency . Building measures for thermal confort include: house type and orientation if you think on a new building, improved insulation in ceilings, walls, floors, doors and windows to restrict conductive heat flow , reduced air leakage to restrict convective heat flow and more passive solar south facing windows. Concerning appliances, you can have more or less efficient cooling and heating systems, lighting or other appliances like refrigerators or washing-machines and, even a solar water heater.

Inputs  Explorations  Assumptions
House Type: House Orientation:
House Size (m2): Electricity Cost:
Gas Cost:
Window Type:
Ceiling Insulation:
not for flats
Door Insulation:
Floor Insulation:
not for flats
Air Leakage:
% South Windows:
North-South case
Lighting Efficiency:
Appliance Efficiency:
Heating System:
Cooling System:
Water Heating:
Annual Electric Bill
Annual Electric Use
Annual Gas Bill
Annual Gas Use
Annual Energy Bill
Annual CO2 Emission ton

Wall construction:
The type of construction used in the walls is brickwork. Select from cavity walls, insulated walls, or extra insulated walls acording to portuguese standards (RCCTE; "Regulamento das Características de Comportamento Térmico dos Edifícios, Dec.Lei 80/2006, de 4 de Abril").
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Ceiling, Floors and Doors:
This input selects the level of insulation used in these parts of the house. Select "low" for a current (in Portugal) building (take the level of the RCCTE reference "U" for I1), "medium" for an insulated dwelling (take the level of the RCCTE reference "U" for I3) , or "high" for well-insulated components, well above the more stringent "U" values of the RCCTE.
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This is how energy efficient the appliances in your home are or can be. Select "low efficiency" for current appliances, "standard appliances" for new ones and "high efficiency" for new appliances with energy-saving features. A low energy system can be selected also. It has "high efficient" appliances powered by alternative technologies. Solar and windpower technologies, mini-hidrics and other alternative technologies can be developed so that, in the future they will be cost-effective, according to local geo-climatic conditions. Architecture and the building form have little to do with this, but...think of the old familiar solar dryer, the laundry on the line in the sunny side of the house. A conservative 50% share of the energy requirements of "high efficient" appliances is considered in this low energy (high + "solar" energy) option.
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Select "low efficiency" for primarily conventional incandescent bulbs and "high efficiency" for fluorescent energy-saver lamps. We include also a no-cost option with photovoltaics. The continuous development of photovoltaic (PV) technology has provided an increase in output and realibility as well as a decrease in cost. So, it is possible that they will be cost-effective in the near future, not only as a stand-alone system in remote sites, but also as a grid-connected system.
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Heating system:
You can select a low or high efficiency gas furnace (select high efficiency for newer models), electric resistance (baseboard) heaters, an electric heat pump, or natural heating (no heating system installed, thinking on more passive solar or a fireplace with a heat recovery device).
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Cooling system:
You can select low or high efficiency electric air conditioning (select high efficiency for newer models), an electric heat pump or natural cooling (no air conditioner installed, thinking on natural evaporative cooling, radiant cooling, ventilation or more thermal mass according to local climatic conditions).
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Select among five window designs: (1) a clear, single-glazed (single-pane) window, (2) a clear, double-glazed window, (3) a double-glazed window with a tinted glass, (4) a double-glazed window with a reflective coating or (5) a double-glazed "passive-solar" window with a special "low-E" film for cold, sunny conditions .
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Percentage of South Windows
Select the percentage of your windows that face south. South-facing windows are generally desirable in the northern hemisphere because they can capture more useful solar radiation in the winter compared to windows with other orientations and they're easier to shade than east- or west-facing windows. If you can have windows on the four sides of a detached house, a window configuration of 25% south-facing means your windows are evenly distributed among north, south, east, and west. A window configuration of 50% means half of your windows face south (as is the case in a lot of passive solar homes). A window configuration of 75% south-facing means that almost all of your windows face south, which might be true in passive solar home designs where a great deal of attention is paid to window orientation. If you have a flat or a row house and a North-South orientation you can choose the amount of South windows, but in the East-West case of flats, row houses or detached houses, the program assumes a fifty-fifty distribution between the front and the rear walls.
Sorry! You can not change the total amount of glazing or choose an indirect solar system (trombe wall or sunspace). Anyway, this systems are not so good energy performers than the direct gain and they have higher inicial costs. Sunspaces are not recommended in most portuguese climatic conditions but can give a beautiful extra lively space with many flowers and even fruits, in cold and sunny winter days.The time-lag of trombe-walls (without vents) can be interesting for bedrooms.
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Water heater:
Select the type of water heater: You can select a low or high efficiency gas water heater (select high efficiency for newer models), electric resistance (baseboard) heaters, an electric heat pump water heater, or a solar water heater.
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Air leakage:
Select whether your home is leaky, average, or tight with respect to air infiltration (leakage).
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There are eight cities representing a range of Portuguese and U.S. climates. Some have exceptionally cold winters and some have mild winters. Some have hot summers and some have mild summers. Climate data and solar radiation data for each city are used in the energy analysis.
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House type:
You can choose amongst three reference cases: a one storey detached house, a two storey house within a row or a flat (one or two storey) within a housing block. This flat is surrounded by other flats, so it has only two exterior walls, the front and the rear wall and no roof or exterior floor. All these reference houses have compact plans. Indented plans will be more energy consumers in Winter and can be also in Summer, depending on local climatic conditions. Special types, as patio and earth sheltered houses, are excluded.
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House Orientation:
You can select a North - South or an East - West house. This choice is important if you have only a front and a rear wall, as is the case of flats and row houses. Select the North -South house if you have a detached home with four exterior walls. You can have also, a detached home with East and West windows only.
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House size:
Select the gross floor area of your house (in square meter).
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Electricity cost:
Select the amount you pay for electricity, euro per kilowatt-hour: on-peak 0.1725, off-peak 0.0946, mix on(14h)/off(10h) 0.143542 (Lisbon, actual cost 2013).
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Gas cost:
Select the amount you pay for gas per kwh : natural gas 0.0772 euro/kwh (Lisbon, actual cost 2013).
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Annual electricity use:
Measured in kilowatt-hours. You find your own home's electricity consumption on your electric bill measured in kwh.
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Annual gas use:
Measured in cubic meter. You find your own home's gas consumption on your gas bill measured in cubic meter in Portugal.
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Annual electricity bill:
This is your electricity bill for all purposes, according to your choices.
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Annual gas bill:
This is you gas bill for space heating and water heating if you choose it, but not for other purposes, namely cooking.
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Annual energy bill:
The sum of your annual electricity and gas bills.
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Annual CO2 emission:
It is your contribution to the Greenhouse effect, in Tons of CO2 produced in the cycle of the energy consumed by the equipement needed to run your house. A share of hydroelectricity is considered, according to the portuguese case.
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Explorations  Inputs  Assumptions

Assumptions  Inputs  Explorations

Este trabalho que não se destina a ser comercializado, foi produzido a partir do documento Whole House Exercise, publicado em 1997, na Internet pela Planet, o qual foi corrigido, desenvolvido e alterado para o adaptar ao caso português.