Comparison of thermal transfer characteristics of wood flooring

Energy and Buildings 70 (2014) 422–426
Contents lists available at ScienceDirect
Energy and Buildings
journal homepage: www.elsevier.com/locate/enbuild
Short Communication
Comparison of thermal transfer characteristics of wood flooring
according to the installation method
Jungki Seo a , Yoon Park a,b , Junhyun Kim a , Sughwan Kim a , Sumin Kim a,∗ , Jeong Tai Kim c
a
b
c
Building Environment & Materials Lab, School of Architecture, Soongsil University, Seoul 156-743, Republic of Korea
Dongwha Nature Flooring Co. Ltd. , Incheon 404-810, Republic of Korea
Department of Architectural Engineering, Kyung Hee University, Yongin 446-701, Republic of Korea
a r t i c l e
i n f o
Article history:
Received 13 September 2013
Received in revised form
23 November 2013
Accepted 28 November 2013
Keywords:
Wood flooring
Thermal transfer characteristics
Laminate flooring
Engineered flooring
Installation method
Ondol
a b s t r a c t
There are two types of installation methods for wood flooring; a floating installation method for laminate
flooring, and an adhesive installation method for engineered flooring. Thermal transfer characteristics
from the floorings show a significant difference depending on the installation method, so this study
focused on the comparative thermal transfer characteristics by preparing mock-up scale. The laminate
flooring and the modified engineered flooring of the Korean Standard were used to conduct the tests.
The tests were set up in two rooms in an apartment in Seoul, and a water heat source was prepared at
45 ◦ C and 75 ◦ C. As a result, the velocity of thermal transfer of the modified engineered flooring using
adhesive was faster than that of the laminate flooring. There was no difference of temperature between
both samples at 45 ◦ C of water supply, but a great difference was shown at 75 ◦ C. Moreover, installing
the modified PE foam helped the floating installation method to develop a thermal transfer performance
comparable to that of the preceding research.
© 2013 Published by Elsevier B.V.
1. Introduction
Recent reports by the Inter-governmental Panel on Climate
Change (IPCC) have raised public awareness of energy use and its
environmental implications, and have generated a great deal of
interest in gaining a better understanding of the characteristics
of energy use in buildings, especially their correlations with the
prevailing weather conditions. The supreme importance of awareness requires for undivided responses at national, regional and
global levels [1–5]. In 2002, buildings worldwide were estimated
to account for about 3% of global greenhouse gas emissions [6]. In
their work on climate change and comfort standards, Kwok and
Rajkovich reported that the building sector accounted for 38.9%
of the total primary energy requirements in the United States, of
which 34.8% was used for heating, ventilation and air-conditioning
[7].
In Korea, 97% of energy resources are imported. The Korean
growth rate of greenhouse gas emission per capita was the highest in the world during 1990–2004. Moreover, 83% of the domestic
greenhouse gas emissions stemmed from energy use in the year
2004. Korea belongs to the second group of nations that require
mandatory reduction of greenhouse gas emissions, starting in
2013. Therefore, Korea is working particularly hard to prepare
∗ Corresponding author. Tel.: +82 2 820 0665; fax: +82 2 816 3354.
E-mail address: [email protected] (S. Kim).
0378-7788/$ – see front matter © 2013 Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.enbuild.2013.11.085
for national measures to reduce energy consumption, and limit
carbon dioxide emissions in the construction industry, which is
responsible for over 40% of all carbon dioxide production. In order
to pursue sustainability in the construction industry, the existing
development-focused construction activities must be transformed
via a new paradigm that focuses on sustainable development,
through the adoption of sustainable policies by the government,
and the development and dissemination of sustainable construction technologies [8–10].
The radiant floor heating system (Ondol) has conventionally
been used in Korea. For floor heating, heat is usually supplied from
boilers installed inside each apartment [11]. Hot water from a boiler
is piped to a floor coil, which is an X-L pipe underneath the floor surface. The thermal storage mass consists of cement mortar, which
replaces the traditional stone slab [12–14]. Residents spend a lot
of their time sitting on floors; therefore, the flooring materials
used should be thermo-physically comfortable [15,16]. The control
of water-based floor heating systems is usually divided into two
parts: a central control, which considers the external conditions,
and individual room control [17].
Park et al. researched the click profile of laminate flooring, by
comparison of click and bonding laminate floorings, especially the
base of the click profile shape, bonding strength and international
patents. A non-glue locking system has been used since laminate
flooring was developed. For environmental reasons, and to save
installation time, manufacturers in Europe and the USA have developed a click profile for laminate flooring. In the past, PVC flooring
J. Seo et al. / Energy and Buildings 70 (2014) 422–426
423
Fig. 1. Installation method of laminate flooring and engineered flooring.
was the main product, but the number of wood floorings in use is
increasing as national income rises, and environmental products
have attracted attention. However, these current trends have led
to an increase in the thickness of flooring materials, PVC to wood
flooring, so that heat losses have also increased, because of the low
thermal conductivity of wood. With problems, many researches
focus on the thermal transfer characteristics of wood flooring, especially on laminate flooring and engineered flooring, which are the
most widely used products in the flooring market in Korea. Laminate flooring is installed by a floating installation method, with
polyethylene (PE) vinyl and polyethylene (PE) foam to make the
floor even. Due to the installation method, a click profile type, there
is no possibility of emitting pollutant caused by resin, so that this
flooring can offer a comfortable indoor air quality. However, heat
losses can occur between the connection gaps; besides, PE foams
have many pores to block the upward heat flow, and that is also one
of the reasons to cause heat loss. In the case of engineered flooring, resins are used to fix the flooring on the finishing mortar, so
this floor system can have high thermal conductivity, because of its
adhesive type. However, the thermal conductivity of this flooring is
lower than that of laminate flooring [18]. Thermal conductivity and
thermal transfer characteristics of a variety of wood floorings were
considered above. In this study, the thermal transfer characteristics
of laminate flooring and modified engineered flooring in the actual
living space was compared. The thermal transfer characteristics of
the modified underlay foam with the laminate flooring were also
determined.
2. Experimental
2.1. Materials
In this research, adhesive installation method and floating
installation method were installed to determine thermal transfer characteristics of those. First type, the floating method, was
constructed with this layer; PE vinyl, modified underlay-foam,
and laminate flooring. The modified underlay-foam has a punched
hole, which results in improvement of heat transfer rate from
a heat source. Second type, adhesive installation method, used
a water-borne epoxy adhesive to install modified engineered
flooring. The modified engineered flooring is a flooring to have
melamine film on the surface to increase the surface strength of
it. Fig. 1 presents the two installation methods. Each of flooring
has a dimension with 7.5 mm × 75 mm × 900 mm of the laminate
flooring and 7.5 mm × 190 mm × 1200 mm of modified engineered
flooring, which meet Korean standard.
2.2. Methods
2.2.1. Test in actual living place
This test was performed in two rooms of the same size, located
in Seoul, Republic of Korea. Room 2 and Room 3 were the test
objects in Fig. 2. To minimize outside influences, every side of the
rooms was constructed to be airtight. The laminate flooring was
constructed by a floating installation method on the PE vinyl and the
Fig. 2. Test plan.
modified underlay foam, and the engineered flooring was installed
by an adhesive installation method, after spreading adhesive on
the mortar floor, and then allowing time to cure the adhesive. The
supplying heat temperature of water was 45 ◦ C, and the temperature variation was measured two times with a time schedule, of
heating for 4 h and turning off the heating for 4 h. Fig. 3 shows the
measuring temperature points. The temperature on the flooring
was monitored at five points, and one point for the indoor temperature 1 m above the flooring. Test was carried out with a six
times cycling. Three times tests of the six cycling were measured
in the condition that the modified engineered flooring, as an adhesive type, was installed in Room 2, and the laminate flooring, as
an assembly type, was done in Room 3, and the other three times
tests were vice versa to minimized the test error. Table 1 presents
a summary of the experiment.
2.2.2. Mock-up test
Equal tests were carried out by thermal environment performance evaluation module in Korea Conformity Laboratories (KCL),
to take accurate measurements, and to confirm any errors caused
by ambient conditions and the location of rooms in the preceding tests in an actual living place. The same specification samples
were used, and two modules made with standard flooring structure were installed. The thermal sensors were set at three points
on the surface of the finishing mortar, three points on the surface
of the flooring, and one point in the air. The condition of the test
room was constantly kept at 20 ◦ C temperature and 50% relative
humidity. The module size was 2 m × 2 m × 1.2 m. In addition, the
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J. Seo et al. / Energy and Buildings 70 (2014) 422–426
Fig. 3. Measuring temperature in actual living space (a) laminate flooring and (b) engineered flooring.
Table 1
Summary of the experiment.
Installation method
Floating installation
Adhesive installation
Flooring type
Subsidiary materials
Installation size
Sampling point
Sampling intervals
Laminate flooring
Modified PE-foam, PE-vinyl
3000 mm × 2700 mm
Surface 5 point, indoor 5 point
10 min
Modified engineered flooring
Water-borne epoxy adhesive
3000 mm × 2700 mm
Surface 5 point, indoor 5 point
10 min
3. Results and discussion
3.1. Test in actual living place
Test results are presented in Fig. 6. The variations of the surface temperature of the flooring and the indoor temperature during
heating time were similar, but this result indicated that the thermal transfer performance of the laminate flooring with modified
underlay foam was significantly improved, comparing to the existing PE-foam [18]. Similar test results were measured by the six
times cycling. The room where the modified engineered flooring
was constructed had a 0.2 ◦ C higher room-temperature, and the
surface of the flooring kept a slightly higher temperature. Therefore,
there was no remarkable difference in thermal transfer performance between the laminate flooring and engineered flooring.
Fig. 4. Thermal transfer characteristics test in mock-up lab.
supplying heating source temperatures of water were 45 ◦ C, which
is the temperature of a district heating type, and 75 ◦ C, which is that
of an individual heating type. The time schedule was planned with
heating for 4 h, and turning off the heating for 4 h, giving 8 h of test
time. Figs. 4 and 5 show the test room, and a structure diagram of
the module system.
Fig. 5. Structure diagram of module system.
3.2. Mock-up test
3.2.1. Thermal transfer performance at 45 ◦ C of heating supply
source
Figs. 7 and 8 show the test conducted in the mock-up lab in
KCL. At 45 ◦ C, which is the supply temperature of a district heating type, the surface temperature of the finishing mortar increased
quickly, which led the surface temperature of the engineered flooring to quickly increase. This is because the thermal conductivity
of the resin used to install engineered flooring is far higher than
that of the components of the laminate flooring, and the resins
were thinly and thoroughly spread on the finishing mortar. The
engineered flooring exhibited better thermal transfer performance
than that of the laminate flooring, technically showing about 2 ◦ C
difference of temperature, particularly at the beginning time. Furthermore, the air temperature of the engineered flooring is higher
than that of the laminate flooring, but not as much as the surface
temperature, because the thermal sensor for air temperature was
not influenced by radiant heating energy, but only air temperature.
It takes a long time for air to heat up, because of the high specific
heat of air, which means that there is no significant temperature
variation at the low temperature of the heat source. However, after
heating off, the temperature of the engineered flooring dropped
sharply; on the other hand, that of the laminate flooring decreased
gradually, due to the heat storage capacity of the underlay foam
under the flooring.
J. Seo et al. / Energy and Buildings 70 (2014) 422–426
Fig. 6. Thermal transfer performances in actual living place.
Fig. 7. Thermal transfer performance at 45 ◦ C of heating supply source by water.
Fig. 8. Thermal transfer performance at 75 ◦ C of heating supply source by water.
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J. Seo et al. / Energy and Buildings 70 (2014) 422–426
3.2.2. Thermal transfer performance at 75 ◦ C of heating supply
source
At 75 ◦ C, which is the temperature of an individual heating
type, similar temperature variations and heat storage capacity were
presented. However, as the heating supply source temperature
increased, temperature changes were distinguishably observed,
and the surface temperature of finishing mortar of the engineered
flooring remained 0.5–2 ◦ C higher than that of the laminate flooring
for a heating period, but the laminate flooring could not reach the
peak temperature for 4 h. The results indicate that differences in the
thermal conductivity of the resin for the engineered flooring, and
the PE-foam for the laminate flooring, brought out the difference
of thermal transfer performance.
4. Conclusions
This research determined the thermal transfer characteristic
according to the flooring installation methods and materials, by
tests in the actual living place, and in a mock-up module lab. The test
results show that the thermal transfer performance of the modified
underlay foam for the laminate floor showed better thermal transfer characteristics than the existing PE-foam. Moreover, when both
of the floorings were installed in an actual living place, no considerable difference of thermal transfer performance was found between
the laminate flooring and modified engineered flooring. However,
thermal transfer characteristic of the modified engineered floor was
slightly higher than the laminate floor as the preceding research
[18]. Lastly, when the temperature of the heating supply source
increased, temperature variations were clearly observed, which
made the air temperature remain high.
Acknowledgements
This work was supported by the National Research Foundation
of Korea (NRF) grant funded by the Korea Government (MSIP) (No.
2008-0061908).
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