Engage in a zero energy project

Design & build

The construction of a zero energy building requires taking into account the energy dimension from the project decision phase.

 

In the case of a new construction, three aspects are particularly important:

  • The potential of photovoltaic production.
  • The orientation of the building to optimize solar gains.
  • Potential access to geothermal resources.

 

When it comes to a renovation project, urbanistic constraints, such as the impossibility of external insulation on facade visible for the street, can be decisive.

Main project steps

Design & build

Economic evaluation of the project

 

Building a zero-energy building is an economically important decision that must be evaluated over a reasonable tenure (25 years on average) and take into account the conditions for financing bank credit.

 

By taking as a reference a building built to the minimum energy standards allowed, it will be estimated, over the period selected, the energy savings expected in the proposed zero energy project. In the end the balance of the savings will have to exceed the additional costs associated with the technical choices of the project: quality of the windows, performance and thickness of the insulators, control of the points of attention …

 

In order to estimate potential gains, the estimate will be based on current energy prices. On the other hand, it will be taken into account that a zero energy building require less powerful and therefore less expensiveheating equipment .

 

In practice, the price of energy varies with the economy and is subject to inflation. In the likely assumption of an upward trend over the next years energy consumption savings will become increasingly interesting : Building a building with very high energy performance can therefore be considered as an insurance against the risk of an increase in the price of energy. It should be noted in this regard that the increase in the carbon tax as plan by COP21 to combat global warming will ultimately lead (2030) to an increase in the gas bill by more than 50%.

 

It should be noted, however, that a zero energy building is not fully protected from changes in the price of energy . In fact, it remains connected to the electricity grid and generally buys the electricity it needs at night or on gray winter days. However, the high cost of this additional electricity is hardly offset by the purchase of surplus electricity returned to the grid on sunny days. In order to minimize this gap, maximum self-consumption rate for photovoltaic energy should be targeted. Thus it is recommended to operate electrical devices when photovoltaic production is at its peak (often in the middle of the day). The management of the heat pumps will be optimized by exploiting the thermal inertia of the building and the domestic hot water tanks will be used for temporary storage.

Building design
for high energy performance

Design & build

1 : Focus on natural inputs

Focus on natural inputs

The building must be designed to make the most of natural resources:
This will reduce glass surfaces on the north facade. Indeed, not receiving directly the sun, they do not contribute to the “greenhouse effect” that naturally warms the home.

 

On the other hand, protecting the south-facing bay windows with sunscreens can help prevent overheating while letting the lower winter sun penetrate.

 

Note that, from an heating point of view, the interior shutters are preferable to integrated shutters which generally weaken the insulation.

Design & build

2 : 
Insulation and airtightness

Insulation and airtightness

The energy performance of a building depends closely on a set of factors that will be carefully studied :

  • The thermal insulation of the building envelope is essential: walls, frames, roofs, foundations. Thermal losses being proportional to the inside / outside temperature difference, the exchange surface must be minimized (compact building) and the insulation coefficient optimized (homogeneous insulation characteristics between elements).
  • Thermal breaks must be avoided. Note that external insulation leaves much less room for thermal bridges than interior insulation.
  • Airtightness is both essential and technically difficult to ensure over the life of the building. In this respect, cast concrete achieves remarkable performance. The installation of the windows frame is a delicate practice that must be controlled at the end of the building with the help of a thermal camera.
Design & build

3 : 
Choice of thermal techniques

Choice of thermal techniques

The choice of the all electric is the simplest because it makes it possible to easily deal with the possible problems of summer overheating . For single-family houses the pellet stove with natural ventilation is a possible alternative but it requires to properly distribute the heat produced in all rooms.

More details on the main equipment :

  • Heat pump (PAC): Air/air heat pumps are the easiest to implement. However, they require the use of an additional thermodynamic water tanks. Geothermal energy is more efficient but also more expensive and cooling problems are more difficult to deal with.</ Li>
  • Thermodynamic water tank: It should be considered when there is no water/water or air/water type heat pump.
  • Controlled Mechanical Ventilation (CMV) with double flow. A double flow CMV ensures a constant renewal of the air by extracting the stale air from the humid rooms and pulsing fresh air in all other rooms. Thanks to its internal heat exchanger CMV double flux recovers more than 90% of the heat of the stale air to warm the new incoming air. It is thus possible to renew the air of a home without cooling it.

Simplicity and durability

It should be noted that simple designs are the easiest to implement and maintain . They are also the most robust. In particular, we will try to avoid technological inter dependencies so that each technical element can be operated independently of the others.
There is no need to invest in sophisticated thermal control systems ; a central thermostat with fixed setpoint is sufficient. Indeed a zero energy building whose heating is cut will lose less than half a degree per day in the middle of winter. The average indoor temperature is therefore extremely stable. It fluctuates naturally between day and night by one or two degrees around a stable average. This behavior results from the CMV effect which balances the cooler outside air by around eight degrees at night and the possible solar gains in the middle of the day.

Design & build

4 : Low energy equipments

Low energy equipments

 

The more demanding zero energy goal requires the use of household appliances and low-energy lighting (A+, A++ or A+++).

 

As a benchmark, note that a European household consumes on average 1800 kWh/year for domestic use (lighting, appliances, televisions and other electronic devices …). If it makes the choice of ultra low consumption equipment (A +++) its consumption can be reduced by a third, which corresponds approximately to the annual production of two photovoltaic panels.

 

We also recommend the use of heat recuperators positioned at the outlet of the shower tray to heat incoming water.

 

Similarly, connecting the dishwasher directly to hot water saves up to 200 kWh per year, without additional installation cost or use constraints.