Heating, Ventilation and Air-conditioning Systems Solutions 1

Question 1-[25 marks] a) Is the heat pump in the picture heating or cooling the inside space? Explain how and why. 13 marks] Indoor Outdoor Heat pump is heating the inside space. [1 mark] Hot refrigerant is flowing from the compressor to the reversing valve then to the condenser located in the inside space. Air is forced over the condenser which picks up heat and passes to the room. Refrigerant then flows to the expansion valve where it drops significantly in pressure and temperature. Refrigerant then passed to the evaporator where it absorbs heat energy from the air blown over it by the adjacent fan. Refrigerant then flows back to the compressor by way of the reversing valve to complete the cycle. [2 marks-deduct 3% marks for any steps in refrigeration cycle not explained] b) What is the best option for heating large open areas and why? What are the limitations of this heating system? [3 marks] Radiant heating systems are the best option to heat large open areas. [1 mark] Radiant heating systems will heat all objects in direct line of sight of the heat source. Convection heating systems that heat the air would have to be very large to warm an open space as the air is constantly being lost to the surroundings and replaced with cold air. [1 mark] The limitation of radiant heating systems is they will heat only objects with line of sight so care must be taken with pillars of buildings and other objects that might prevent radiant heat from getting to the areas needed. (1 mark) c) With the aid of a sketch describe and discuss two systems based on the refrigeration cycle that can be used to heat or cool a single indoor space. [4 marks] Any of wall unit, single split, single fan coil or AHU, Chilled beam. mark for system name and 1 mark for correct sketch x 2 systems) d) With the aid of a sketch describe and discuss three different systems based on the refrigeration cycle for heating multiple indoor spaces. [6 marks] Any of multi-split, ducted air, multiple fan coil or AHU, hydronic. 11 mark for system name and 1 mark for correct sketch x 3 systems) e) Describe direct and indirect heating/cooling systems in terms of their primary energy use and explain the fundamental differences? [3 marks) Direct heating/cooling systems convert the primary energy to heat energy in the space being heated or cooled. (1 mark] Indirect systems convert the primary energy to heat energy in a central location remote from the individual spaces being heated/cooled and pass/remove energy from an intermediate fluid (liquid or gas) which transports or removes heat energy to/from the individual conditioned spaces. [2 marks] c) Determine the size of all internal piping for the apartment furthest from the water main connection. Present a table in your answer booklet similar to the example below. Show the working of all steps required to calculate the solution. Index length and allowable pressure drop from previous question, 80m/20m head table [1/2 mark [10 marks] Pipe Section Loading Units PSFR (tres/s) Nom. Size DN () AB 28 0.45 25 BC 6 0.20 20 CD Washing machine (3) 0.20 20 CE Laundry Trouth (3) 0.12 18 BF 22 0.40 25 FG 6 0.20 20 GH Sink (3) 0.12 18 GI Dishwasher (3) 0.20 20 FJ 16 0.34 25 5 0.18 20 KL WC (2) 0.10 18 KM E 0.14 18 MN Basin (1) 0.10 18 MO Shower (2) 0.10 18 IP 11 0.28 Bath (8) 0.30 20 PR 3 0.14 18 RS 20 OR 25 PQ Basin (1) 0.10 18 RT WC (2) 0.10 18 Shower N [K mark each row] Bania K WC Trough Washing D machine Bath Basis WC R HSink Dishwasher f Discuss the advantages and disadvantages of one, two and four pipe heating and cooling systems. [6 marks] System Advantages Disadvantages 1 pipe Lowest cost solution. Last space connected to the system receives or removes less energy than the first space 2 pipe All spaces connected receive or remove close to the same energy Can only heat or cool at any one time-not both 4 pipe Can heat and cool different spaces at the same time Can only heat or cool at any one time-not both Most expensive solution. Requires 2 heat producing/removing devices to heat and cool at same time. [1 mark per point up to a maximum of 6]