How to get cost-effective summer comfort? Passive House Guide

1. Introduction

The summer comfort in buildings was and is still highly underestimated. Over the last century, the efforts to improve the thermal comfort in buildings have been focused on the thermal comfort during winter. Since the beginning of the century, more and more attention has been paid to the summer comfort of the buildings. Different solutions and approaches for cooling of the buildings were developed, many of which are less effective or too expensive. At the same time, cooling costs in Central and South Europe reached the levels of heating costs during winter.

To ensure the summer comfort, the Passive House Institute has developed the PHPP, so summer comfort can be calculated with high precision. These calculations are an excellent tool for Passive House designers because they allow optimized, functional and cost-effective design to achieve summer comfort.

2. Approaches in the Certified Passive House in Sofia

Achieving summer comfort is now extremely important, and it must fully satisfy the occupants. At the same time, the achievement of summer comfort should not burden the project costs, as well as the subsequent maintenance costs.

2.1 Choice of construction

The massive construction assures high specific capacity of the building which results in savings of 2.3 kWh/(m2a) for cooling demand. Due to the large heating capacity of the building, the indoor daily temperature fluctuations are extremely slow and at night the temperature of the air aligns with the temperature of the external walls.

2.2 Careful design of permanent shading elements

Vertical shading elements are calculated for maximum winter and summer comfort. During summer they don’t allow the penetration of high midday summer sun and during winter assure all-day penetration of the sun which results in savings of 3.5 kWh/(m2a).

Compared to 90° reveals, the use of canted on 30° lateral and top reveals is equal to a 7cm thinner wall were used also.

2.3 Careful design of temporary sun protection

To ensure maximum external and internal comfort, tents with automatic control are used on all southern windows. There are other solutions as window shutters, exterior blinds and more but it is important to think always for their operation and the occupant comfort before taking the proper decision. The temporary sun protection results in savings for cooling demand of 8.4 kWh/(m2a).

2.4 Careful assessment of passive night ventilation

All openable windows are equipped with mosquito nets and are provided for double-opening opening. For the night ventilation are used two opposite window located on the 2nd and 3rd floor so used the chimney effect and this saves 3.8 kWh/(m2a).

Figure 1: Air-to-air heat pump connected to the heat recovery ventilation system.

Figure 2: tents with automatic control

2.5 Well insulated hot pipes

Good insulation on the hot pipes within the building envelope leads to double savings:

  • reduced energy losses from the distribution system
  • reduced cooling load from the reduced internal heating load

The insulation of the hot pipes results in savings of 8.3 kWh/(m2a).

2.6 If necessary – careful selection and sizing of an active cooling system

A small air to air heat pump with a capacity of 10,000Btu (Figure 1) was chosen for cooling and heating, which fully satisfies the estimated heating and cooling load of the building at a very reasonable price. There are two main benefits from the system which result in savings of 7 kWh/(m2a):

  • constant supply of fresh chilled or warm air, free of noise and currents
  • additional supply of oxygen to the living rooms at the time of their use, due to the additional recirculation of the air

2.7 Optimal and informed operation of the building

The informed approach and the conscious use of means to achieve summer comfort is crucial. The occupants are to be aware of the use of the night window ventilation, MHRV and temporary shading elements. If a proper operation of the components is used it can reduce the price for cooling in a half.

3. Conclusion

The right solution for achieving cost-effective summer comfort is an integrated design aimed at the Passive House standard. This results in maximum summer comfort, with minimal construction and maintenance costs. The combined effect of all mentioned measures on the cooling load is even bigger – it is 45 kWh/(m2a).

Summary: This article shows the advantages of the integrated design in approaching summer comfort with the Passive House Standard. An innovative approach for heating and cooling with an air-to-air heat pump, integrated into the MVHR is used, allowing high and cost-effective comfort.


[Sibile, Malzer 2015] Sibile E., Malzer H.: How energy-conscious planning lowers construction costs. In: Feist, W. (ed.): Proceedings of the 19th International Passive House Conference 2015 in Leipzig. Passive House Institute, Darmstadt, 2015.

[Mikeska 2016] Mikeska, T.: Concept of Passive House Institute Certification for split-type air-to-air heat pumps. In: Feist, W. (ed.): Proceedings of the 20th International PH Conference 2016 in Darmstadt. Passive House Institute, Darmstadt, 2016.

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