Is high insulation in summer useful for the sector residential?

Increase insulation in buildings in summer? Does it bring advantages?

It is well known that one of the most effective methods for to reduce the demand for heating is to have of a high insulation in the envelope of the building . Sometimes this high isolation is questioned – by some technicians – considering that it might not be useful or counterproductive for reduce cooling demand.

It is true that to reduce the demand for refrigeration the key elements are sun protection and adequate air transfer management (infiltration, ventilation natural, mechanical ventilation).

We will not deal in this article with the cost relationship benefit (economic / environmental) that each one of the measures (sun protection / management of the air transfer/insulation level increase) by what from this article it will not be possible to conclude which measure is the priority to adopt since this is an issue that only can be addressed on a case-by-case basis.

But... Is a high level of isolation useful to reduce cooling demand? Is it useless in any case?

Method

We will consider an intermediate dwelling of a multi-family building so that it is not very demanding of refrigeration (not the top floor of a building).

We will calculate the cooling demand with several levels of insulation (from zero to 20 cm of insulation) considering the four main orientations (South / West / North / East) and located in four geographical locations of the Spanish state (Barcelona / Madrid / Las Palmas / Seville).

Programs used:

• Sketchup Program . For the creation of the geometric pattern.
• OpenStudio program . For the energy modelling. With some specific macros for facilitate the introduction of natural ventilation controlled and of the economizer in the calculation of the demand.
• jEplus program . to facilitate the generation of multiple calculation hypotheses (5 levels insulation * 4 orientations * 4 locations = 80 cases) and the subsequent tabulation of the results for their analysis.

The results will be compared for each site using as an indicator the percentage reduction in the demand for cooling in relation to what the building would have without any type of isolation but that he enjoyed in all cases maximum sun protection and management optimization of ventilation.

Geometric Model

Intermediate floor in a house multi-family house between party walls with a façade front and a rear, a patio of lights and a skate of ventilation of bathrooms shared with other dwellings in the same building.

• Useful surface area: 114.51 m2
• Volume : 343.54 m3
• Front facade : (7.29+0.44)*3= 23.19 m2 with holes 1.1*2 and 2.7*2 that represent 32.77% of the surface.
• Rear Facade : 7.29*3= 21.87 m2 with 1.24*2 and 1.2*2 holes that represent 22.31% of the surface.
• Facade of light wells : (0.88+3.83+2.08)*3=20.37 m2 with holes 0.9*1.2 and 0.9*1.2 that they represent 10.60% of the surface.
• Skate facade bathroom ventilation : (0.76+1.06+0.76)*3=7.74 m2 with holes 0.4*0.7 and 0.4*0.7 that they represent 7.24% of the surface.

• Orientation . Four are considered orientations with the main façade to the South / West / North / East.
• Constructions, shafts and bridges thermal . The descriptions used are detailed in Tables from HERE (A window opens to see it better).
• Boundary Conditions . The facades: front, rear, of the patio of lights and of the skate are considered exterior the rest of the enclosures are considered adiabatic (in contact with other dwellings).

• Own shadows . The building has a balcony on the front façade (See balcony window) and another in the later. They provide some shade over the façade, the walls that enclose the patio of lights and the skate will also provide certain shadows in the corresponding facades.

• Other people's shadows . It is considered that the nearby buildings are far enough away that cast shadows on the dwelling under study.
• Internal loads. Occupation : Se consider some internal loads derived from the occupation (people) with an occupancy rate of 20 m2 /person and a activity of 70W/people, the hourly profile follows the scheme which is described in the following graph.

Occupancy is maximum (400 W and 5.7 people) at night of all days, it is also maximum on weekends and reduced in the morning (100 W and 1.4 people) and intermediate (200 W and 2.8 people) in the central hours of the days weekdays.

• Internal loads. Lighting : The illumination corresponds to a maximum level of 4.4 W/m2 during dusk hours greatly reduced during the night and medium in the central hours of the day.

There is no differentiation between weekdays and weekends of the week.

• Internal loads. Electrical equipment : The teams have exactly the same definition as the lighting.
• Summary definition of loads and transfer of air (infiltration + ventilation). In the table following can be seen the definitions of loads and air transfer rates used in modeling the building.

This definition of loads and their hourly profiles are identical to those prescribed by the DB HE for homes.

• Thermal inertia : For the calculation, Considering that the internal thermal inertia is 20kJ/m2, This value is intended to represent the accumulation capacity of heat from elements not explicitly entered into the model (furniture and partitions) since the one introduced by the elements of the envelope (facades / floor / ceiling) are already introduced directly and explicitly through the constructions used
• Air transfer : Infiltration + mechanical ventilation + natural ventilation. has been considered a constant air infiltration equivalent to 0.2 ACH during all
  days and hours of the year (blue line in the attached graph). Of interest see the article on control systems air conditioning and how aerothermal energy works.

For mechanical ventilation, a flow rate of air of 4l/s/person (following the occupancy profile) and the effect of an air economizer on the IdealLoad system, which It is activated whenever there is a cooling demand and the outside air has a temperature below the temperature indoor air (red line in the graph).

Controlled natural ventilation has also been considered of 4 ACH during any time that the temperature inside is higher than 25ºC and that the outside air is more colder than the indoor temperature (green line on the graphic)

The attached form reproduces the definition of this “controlled” ventilation to take advantage of the possibilities of free cooling when the indoor temperature tends to rise and simultaneously the outside air has capacity refrigerator.

This way of proceeding minimizes the demand for cooling by optimizing heat transfer air.

• Sun Protection . It has been considered a sun protection system (blinds) consisting of reduce the solar factor of the shaft by 70% provided that the internal temperature rises above 25ºC and that the incident solar radiation on the hole exceeds 75 w/m2, in this way, sun protection is maximized in those moments that are necessary to minimize the demand for cooling without affecting the heating demand.

The attached graph shows how the solar transmittance of a hole when solar radiation is greater than 75 w/m2 and the interior temperature rises by above 24ºC.

• Setpoint temperatures . It has been considered a constant setpoint temperature of 26ºC for cooling and 20ºC for heating.

• Climatology . Three have been considered climates for the calculation representative of the areas Seville / Madrid / Las Palmas / Barcelona.

• Calculation of energy demand . HE calculates the energy demand for both heating and cooling for each of the case studies (location/orientation and level of insulation) considering a set point temperature constant of 20ºC for heating and 26ºC for refrigeration.

Inclusion of the IdealLoad system to calculate the demand.

Included in the IdealLoad system is a system economizer that allows to increase the rate of outside air when it is “fresh” in relation to the indoor air and the enclosure requires refrigeration, thus optimizing the ventilation management to minimize the demand for refrigeration.

Analysis of results

The following graphs show the increase in reducing the cooling demand for each location depending on the different orientations and the thickness of the insulation used.

Conclusions

• It can be clearly seen that in all cases the maximum insulation thickness provides maximum reduction of cooling demand so increasing insulation in buildings is not only not counterproductive in summer regime, but it is always favorable to reduce demand.
• Increased insulation is more effective in East and West orientations because they are the most unfavorable in the summer regime from the point of view of reduce cooling demand.
• In Barcelona and Las Palmas there is a greater differentiation between East/West orientations in relation to the North/South orientations than in the other sites considered
• In the most exposed houses (for example, under cover) from a demand point of view of refrigeration, the beneficial effect of increasing isolation will become even more evident.

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