We summarize the basic techniques used to save energy in a greenhouse and discuss the development of a new energy-saving pipe-framed greenhouse, similar to the type used on most small-scale farms in Japan. To enhance the thermal insulation performance of a pipe-framed greenhouse, a multi-layered thermal curtain was installed. As a result of our experiments, both the heating load and the heating oil consumption in the greenhouse with a multi-layered thermal curtain (M-house) were approximately 40% lower than those in the control greenhouse with a conventional thermal cover (C-house). Furthermore, the heating oil consumption was also reduced by approximately 60% in the M-house equipped with water heat storage, which stored solar energy in daytime and released heat to the greenhouse at night. This multi-layered thermal curtain is expected to gain recognition as the most effective energysaving material available and immediate widespread use nationwide is expected. Another experiment was performed concerning the structural reinforcement of pipe-framed greenhouses. Pipe-framed greenhouses are usually constructed with single-arch pipes in Japan and there has been a recent increase in greenhouses collapsing due to strong winds. Accordingly, techniques to reinforce the structure of pipe-framed greenhouses were also developed. Discipline: Horticulture Additional key words: heating load, heat transmission, multi-layered thermal curtain *Corresponding author: e-mail hirokik@affrc.go.jp Received 31 March 2014; accepted 24 December 2014. Introduction In Japan, greenhouses used for protected horticulture take up an area of approximately 50,000 ha, about 40% are equipped with a heating system and more than 90% depend on fossil fuel. In Japan, protected horticulture is responsible for 45% of all carbon dioxide emissions (about 611 million tons) derived from fossil fuels used for agriculture, forestry and fisheries (Hayashi 2008). Most fossil fuels are used in protected horticulture for heating oil and the amount of fuel consumed for this purpose increased about 2.2 times from 1990 to 2005. Energy costs have also been steadily increasing, which has become an important factor influencing the management of farms. Accordingly, it has become necessary to develop energy-saving techniques for protected horticulture. In Japan, approximately 80% of all greenhouses are high-tunnel and high tunnel-like greenhouses; these are referred to as pipe-framed greenhouses, where the frames are constructed from steel pipes. The high tunnel, where sidewalls are not round like a hooped house, has no electrical service, automated ventilation or heating system (Lambert 2009). This review focuses on pipe-framed greenhouses in Japan with a heating system and other environmental control equipment. Basic energy-saving techniques for greenhouses have been classified into three groups: 1) reducing heating load, 2) introducing a high-efficiency heating system and 3) temperature management, namely, varying night temperature control, local air heating, the usage of cultivars for low-temperature tolerance and so on (Hayashi 2008). These techniques are usually used in combination. The key energy-saving technique in greenhouses involves reducing heating load or loss by installing a fixed or movable covering, an air-inflated covering, etc. (Naito 1981). Overnight, heat loss from greenhouses occurs due to overall heat transmission through coverings and structures. It is also caused by air infiltration and heat flux of the inside-air to the soil, although this is reversed in some cases. Heat transmission accounts for a large part of the total heat loss from a greenhouse, followed by heat transfer due to air