Thermal Efficiency, Mixing Loss and Energy Saving Index of VAV Systems

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  • VAV方式の熱効率・混合損失・省エネルギ指数
  • VAV ホウシキ ノ ネツ コウリツ コンゴウ ソンシツ ショウエネルギ シス

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Abstract

In this report we calculated annual cooling and heating coil loads, thermal efficiency, mixing loss and energy saving index of VAV systems and compared them with those of 4-pipe induction unit system in perimeter zones of model building. The hourly heating and cooling loads for 365 days of year were calculated with aids of HASP/ACLD 7101 and the standard meteorological data in Tokyo by SHASE. For the minimum flow rate of outlet air of VAV systems, two values, that is, 50% of the maximum flow rate and the greater one of 25% of the maximum and the minimum outside ventilation air (6m^3/m^2・h), were set and computed respectively. For all systems, the load was calculated in following three cases: employing neither rotary type air to air heat exchanger nor free cooling (Case 1); employing the exchanger with 70% efficiency, but not free cooling (Case 2); and employing both the exchanger with 70% efficiency and free cooling whenever possible. The cooling energy saving index is defined as follows: CESI=(q_C)/(Q_C), CESI'=(q'_C)/(Q_C), CESI"=(q"_C)/(Q_C) and the heating energy saving index-as follows: HESI=(q_H)/(Q_H), HESI'=(q'_H)/(Q_H), HESI"=(q"_H)/(Q_H) where q_C: annual cooling coil load of one zone q_H: annual heating coil load of one zone Q_C: basic annual cooling coil load Q_H: basic annual heating coil load (') and (") show the value of Case 2 and Case 3, respectively. As the basic coil loads, in this report, we adopted the mean cooling and heating coil loads of Case 1 of 4-pipe induction unit system in the perimeter zone. As a result, VAV systems of Case 3 obtained more energy saving than 4-pipe induction unit system, when the minimum flow rate of supply air was set at 25% of the maximum air and speed control was adopted at supply fan.

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