Reviewing the window performance indication system for improvement of housing energy eficiency performance in 2030

1. Review of Indication Method

(1) Issues of the conventional indication method
In the current form of window distribution, sash manufactures ship sashes and glass manufactures ship glasses, and intermediate agents and distributors combine them to ship as windows to building contractors in many cases. Many of these agents and distributors feel it a burden to calculate window performance and stick performance indication labels. In the current window performance indication system, sticking the performance indication labels to the products has been hardly disseminated.

 

(2) Review of the indication method
Based on the actual situation mentioned above, as with the conventional system, the sash and glass manufacturers shall take currently available measures; (1) publishing in a catalog (including a website) and (2) indicating at an exhibition site such as a showroom.

About sticking of the performance indication labels to the window products, on the other hand, it is expected that their exposure to more consumers raises their awareness of the windows with high thermal insulation, thereby disseminating higher-performance windows not only in newly built houses, but also in the existing ones.

For this reason, the intermediate agents and distributors also look to stick the performance indication labels to the products as much as possible by receiving supply of the easily and accurately stickable performance indication labels as well as improving skills required for performance calculation and introducing support tools.

(After revisions)

2. Review of Indication Items based on Revisions of JIS

JIS A 4706, which has been referred to in the conventional window performance indication system, was revised in February 2021, newly adding higher grades of thermal insulation and evaluation indexes for solar radiation heat acquisitiveness (see within bold lines in Fig. 1).

(1) Addition of grades for thermal insulation performance
Along with these revisions of JIS A 4706, allocation of stars showing thermal insulation performance of windows shall be indicated in 6 levels based on the following concepts 1) to 4), specifically reviewing current allocation of stars as shown in Fig. 2.

<Concepts of new allocation of stars>
1) Allocate star indications in an easily understandable manner to the consumers and so that the higher grades newly added to the JIS A 4706 can be evaluated.
2) Assuming*1 that the overall heat transmission coefficient 2.3 [W/(m2・K)] will be an average performance value in the market in the near future, prevent the indication of the said performance from exceeding the half of six stars.
3) From a viewpoint of promoting dissemination of windows having politically targeted thermal insulation performance, ensure that the indication of Grade H-6 (1.9 [W/(m2・K)] ) has more than half of six stars, whose performance excels the overall heat transmission coefficient 2.08 [W/(m2・K)], so as to be consistent with the target standards of the Top Runner Program for building materials calculated based on thermal insulation performance of housing in 2030.
4) In view of the current average thermal insulation performance value (about 2.6 [W/(m2・K)] of windows in the market, ensure that performance below average can be evaluated in a phased manner to some extent by means of star indication.
*1: The overall heat transmission coefficient 2.3 [W/(m2・K)] is achievable by sashes with aluminum resin composite or above, and they have been already marketed at a substantial ratio (about 75%).

 

(2) Newly added indication of solar radiation heat acquisitiveness
As JIS A 4706 has newly established the evaluation indexes for “solar radiation heat acquisitiveness”, the numerical values of the “solar radiation heat acquisition rate” and 3 levels of grades according to the said numerical values shall be indicated as follows (three marks indicating a solar radiation amount (Fig. 3) sequentially respond to N-1 to N-3 from the left, respectively; the left-side mark, for example, indicates the solar radiation heat acquisition rate of over 0.50 up to 1.00).

Concerning the solar radiation heat acquisitiveness, appropriate windows may change depending on the region or direction. Accordingly, it should be avoided for its designation to give the impression to the consumers that a higher numerical value or a higher solar radiation amount mark is simply better. For this reason, “solar radiation heat acquisition rate” shall be used as a designation instead of “solar radiation heat acquisitiveness” which may remind consumers of “performance”.

Since the “solar radiation heat acquisition rate” has not been fully understood by the consumers at this moment, a “Guidance for Window Performance Indication Labels” mainly consisting of the following items shall be prepared in cooperation with relevant industries and supplied together with “solar radiation heat acquisition rate” indication labels to the consumers, and sales representatives, designers, etc. who are expected to explain to the consumers, thereby developing their understanding.

Fig. 3. Draft Design of Solar Radiation Heat Acquisition Rate Indication Label

 

Fig. 4. Design of Window Performance Indication Label (Vertical Design)

 

Fig. 5. Design of Window Performance Indication Label (Horizontal Design)

<Outline of the “Guidance for Window Performance Indication Labels”>
1) Background and purpose of formulating the Guidance
2) Guidance target, etc.
3) Thermal insulation performance of windows (Importance, advantages, viewpoints, etc. of “thermal insulation performance” of windows)
4) Solar radiation heat acquisition rate of windows (Importance,1) advantages/disadvantages, viewpoints, etc. of “solar radiation heat acquisition rate” of windows)
5) Preparer’s credit
6) Operation of the Guidance

Particularly, “Guidance for Window Performance Indication Labels” shall mention that “acquisition of solar radiation heat” has an advantage of decreasing the heating load in winter on one hand and has a disadvantage of increasing the cooling load in summer on the other hand, and to the contrary, that “shielding of solar radiation heat” has an advantage of decreasing the cooling load in summer on one hand and has a disadvantage of increasing the heating load and lowering visible light transmission in winter on the other hand, and shall additionally provide careful explanations as to what values are appropriate depending on the region and direction, appropriate balance between acquisition and shielding of solar radiation heat according to the living style and concept of values, and possible impact on thermal insulation performance.

(3) Design of the indication labels
Combining (1) thermal insulation performance and (2) solar radiation heat acquisition rate mentioned above, two types of label designs shall be introduced and either one may be used; the details of indication items and their layout are shown in Fig. 4 and Fig. 5. Considering the burden of preparing the labels at the time of sticking them to the products, it shall be allowed to use those without the numerical values of the overall heat transmission coefficient and solar radiation heat acquisition rate.

4. Proposal for Future (Utilization of WEP Method)

The conventional window performance indication system has referred to JIS A 4706 so far. In addition, the method for calculating energy performance (JIS A 2104, so-called WEP method) is being enacted as a new standard in consideration of thermal insulation performance, heat shielding performance, airtightness, daylighting performance, etc. of windows.

However, since JIS A 2104 (WEP method) changes performance values (WEP values) depending on the region, direction, building model, etc., it is not easily understandable to general consumers, and its calculation method has not disseminated even among experts.

In addition, in the case of utilizing this as window performance indication in the future, it is necessary to mainly consider the following items such as setting of thresholds for performance grade categories.

1) Method for setting the thresholds for the grade categories
2) Relations with utility bills and their calculation method
3) Relations with regional categories and their indication standard
4) Method for setting the typical direction and building model in calculation

Because of these items, it is conceivably too early at this moment to utilize the WEP method as window performance indication. On the other hand, given that indication of the solar radiation heat acquisition rate has been newly added this time as described in 2 (2), it is similarly important for the consumers to deepen understanding of relations between energy efficiency performance and window performance of housing in the future. In this respect, it is significant to seek after utilization of the WEP method.

Accordingly, on the premise of developing unified operation rules, etc. for JIS A 2104 (WEP method) in the industry so as not to confuse the consumers, the business operators shall not be obstructed from voluntarily utilizing it for window performance indication.

5. Realization of 2030 Energy Efficiency Goal in Housing and Building Sector

In order to achieve the energy efficiency performance goal for houses to be newly built after FY2030, high thermal insulation of houses is important. Particularly, it is significant to ensure the consumer’s correct understanding of window thermal insulation performance, etc. and develop an environment allowing selection of appropriate windows through the new window performance indication system, because most of the heat comes in and goes out of openings such as windows.

For this reason, the government, manufacturers, etc. (sash and double-glazed glass manufacturers, house manufacturers engaged in manufacture and assembly of windows, and processors and importers such as intermediate agents and distributors) and users (end consumers, design offices, homebuilders, building contractors and builders) shall address the following.

(1)Approaches by the government
1) In cooperation with the manufacturers, etc., enlighten dissemination of the window performance indication system to the consumers, including improvement of awareness, adequate utilization method.
2) For the newly introduced “solar radiation heat acquisition rate”, prepare supplementary materials helpful for the consumer’s understanding in cooperation with the manufacturers, etc. and provide them for the consumers together with indication of the “solar radiation heat acquisition rate”, thereby developing the consumer’s understanding as to the point that it is important to consider acquisition and shielding of solar radiation in order to secure energy efficiency performance of housing.
3) For sticking of the window performance indication labels to the products, higher consumer’s awareness will help efficient dissemination of higher-performance windows and allow the consumers to confirm window performance of the existing houses. Accordingly, make efforts to stick them to the products as much as possible, and urge the manufacturers to support intermediate agents and distributors in improving calculation capabilities and introducing support tools.

(2)Approaches by the manufacturers, etc.
1) Make efforts to utilize window performance indication in every opportunity by such as posting it in catalogs and putting it up in display home villages, etc.
2) For sticking of the window performance indication labels to the products, higher consumer’s awareness will help efficient dissemination of higher-performance windows and allow the consumers to confirm window performance of the existing houses. Accordingly, make efforts to stick them to the products as much as possible.
3) When this is done, the sash and double-glazed glass manufacturers support the intermediate agents and distributors in improving performance calculation capabilities, introducing support tools and providing easily and accurately stickable labels.
4) For the newly introduced “solar radiation heat acquisition rate”, prepare supplementary materials helpful for the consumer’s understanding in cooperation with the government and provide them for the consumers together with indication of the “solar radiation heat acquisition rate”, thereby developing the consumer’s understanding as to the point that it is important to consider acquisition and shielding of solar radiation in order to secure energy efficiency performance of housing.

(3)Approaches by the users

1) Make efforts to select appropriate windows through utilization of the window performance indication system, etc. to secure energy efficiency performance of housing.
2) For the designers, provide information for general consumers so that appropriate windows will be selected in designing and constructing the houses.

Conclusion

To achieve the government’s energy efficiency goals in the household and commercial sectors mentioned in the Basic Energy Plan, etc. toward realization of carbon neutrality in 2050, high thermal insulation of houses and buildings is important. Particularly, most of the residential heat comes in and goes out of the openings such as windows, and furthermore, higher window performance is expected to have a sound insulation effect, etc. In seeking after a better housing environment, accordingly, it is necessary to take measures contributive to higher window performance.

Concerning this point, the supply side has enhanced the Top Runner Program for building materials of windows (sashes and double-glazed glasses) prior to this summary. Together with this, however, the government and manufacturers, etc. need to share the recognition that it is extremely important for the demand side to take measures as well, and develop awareness that it is essential to improve thermal insulation performance of the openings by utilizing the window performance indication system and enlightening its dissemination to the consumers for realization of a better housing environment, thereby urging the consumers to independently select better windows.