Eco Cute case study: shifting hot water production to night time

By team, Aug 24, 2011, 15:38 3 minute reading

A business hotel in Tottori, south-west Japan, has opted for a hot water system based on commercial Eco Cutes to achieve energy efficiency and low running costs. A common bathing area has helped shift hot water demand patterns, taking full advantage of the heat pump system characteristics.

The Tottori Green Hotel Morris is located in front of the JR train station in the city of Tottori, in the prefecture of Tottori, south-west Japan. Its construction finished in December 2009 and the hotel opened its doors to customers in January 2010. The hotel accommodates mainly business travelers but also tourists.

The 8 storey and 6,406 m2 building has 213 rooms and was built according to the “all-electric” principle, featuring commercial Eco Cutes for hot water production in addition to small size electric water heaters, as well as air-source heat pump chillers and room air-conditioning and of course all-electric kitchen appliances.

Shifting hot water demand patterns

Hot water demand in a business hotel is particularly high in the mornings and evenings. One of the means identified to save energy was therefore a redistribution of the hot water demand in peak hours. The solution the business hotel opted for was a common bathing area, which perfectly fits into the Japanese bathing culture.

The common bath is filled between 1-3 pm and uses the water heated up over night by the Eco Cutes. The water is exchanged only once per week, however in winter time it needs daily re-heating. Energy consumption during filling the common bath increases to 850 MJ/h.

The main part of the hot water is heated with the Eco Cutes over night, between 10 pm and 8 am. As soon as the water level in the tanks drop below 50% however, the electric water heaters kick in to heat up additional hot water.

The dark gray part is the amount of water heated up by the heat pumps. The white part below is the stored water in the tanks, the white part above is the water used at a particular time.

The system consists of
  • 5 commercial Eco Cute units with an average capacity of 40-56 kW with a COP of 4.10. At ambient temperatures of 16°C DB / 12°C WB the water is heated from 17°C to 65°C. At lower ambient temperatures of 2°C DB / 1°C WB, the capacity is 40 kW with a COP of 2.45 and the water is heated from 5°C to 65°C.
  • 2 water tanks of 20 cubic meters
  • 3 small sized electric water heaters
  • 2 hot water circulation pumps, pumping the water from 2-6th floors
  • 1 hot water booster pump, increasing water pressure in 7-9th floors
  • 1 filter pump

Substantial CO2 emissions reductions

The case study was carried out shortly after the hotel had opened its doors and empirical data had therefore not been available yet. Simulations however calculated possible CO2 emissions savings of the Eco Cute hot water system at 48.7% (91.1 tons CO2/year) as compared to a gas boiler hot water system (139.8 tons CO2/year).

The same simulation calculates ~€14,000/year running costs for the Eco Cute hot water system versus ~€45,270 for the boiler system. Running cost savings counterweights the higher acquisition costs for the Eco Cute system that is currently almost three times higher than for the boiler system (~€226,355 vs ~€86,000).

The main disadvantage of the Eco Cute system however is that it takes twice the space and is twice as heavy as a boiler system with the same capacity.


By team (@r744)

Aug 24, 2011, 15:38

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