B4. (a) A screw type chiller plant is designed for an office building with 1000 kW refrigeration capacity. It operates in an ideal vapour compression refrigeration cycle. Assume both degrees of sub-cooling and superheating are
2\deg C
. The evaporating pressure and the condensing pressure are 0.2 MPa (absolute) and 1 MPa (absolute) respectively. With the aid of a p-h diagram, calculate the mass flow rate of refrigerant in
k(g)/(s)
. (5 Marks) (b) In the replacement of a room air conditioner for a domestic flat, the contractor has proposed the use of a unit with R32 as refrigerant on the ground that there is no control of such usage. Comment on the proposal and discuss whether such use can be accepted. (5 Marks) (c) With the aid of Table B4 and the following information, design a supply air diffusion system for a room with the determination of minimum number of diffusers and neck size. State the precautions taken. Office dimensions:
50m(L)\times 20m
(W)
\times 2.4m(H)
Total supply air flow rate:
3.15(m^(3))/(s)
(equally distributed through the diffusers) Supply air outlet:
600mm\times 600mm
(face dimensions) Design criteria for supply air outlets: Linear dimension D , served by 1 diffuser
<3x
ceiling height Ceiling diffuser pattern
(D_(max))/(D_(min))<1.3
Neck velocity of supply air outlets
<4(m)/(s)
NC<30
(10 Marks) To be continued...