AIR CONDITIONING
VRF: not just a stand alone system
Martyn Ives, head of technical, Fujitsu General Air Conditioning UK, looks at the versatility of VRF systems.
W
e think of air conditioning as being standalone – a method to cool our occupied space. End- user perceptions vary from transferring air between outdoor unit and indoor unit to slightly more accurate connotations of energy transfer. Most of us in the industry have some knowledge of how this transfer works and the refrigerant cycle involved, but are we aware of the opportunities aside from ‘cooling a room’?
The history of air conditioning is well documented across many sources and its development is generally based on the discovery of other technologies or elements, as with most things. It is quite surprising that in the majority of cases end-users believe air conditioning is only for cooling, when in fact heat pumps have been available since around 1977, producing both cooling and heating effects. It is here that our understanding and industry knowledge becomes far greater than those outside of the sector. We understand about heat pumps, heat recovery, the transfer of energy, the high efficiencies and its uses. But do we understand its design potential as well as we should, now the heat pump has had 42 years to develop?
When we look at buildings’ functions and features, we see a mixture of services. Air conditioning that regulates the building temperature, boilers generating the hot water, and air handling units, introducing fresh air whilst removing the stale air and keeping CO2
levels acceptable. All require their
own sources of energy, be that gas or electricity. Through understanding a VRF heat recovery system, accompanied by
some informed planning during design stage, energy recovery can be realised across many different types of products. Taking air handling units as an example, these could include a direct expansion or hydronic coil to provide either the tempering of fresh air or extend to full air treatment. Whilst integrated heat pumps are an option, an external air conditioning system can be applied to serve a direct expansion coil within the AHU. Wide operating envelopes allow the DX coil to work with supply air temperatures down to -7o°C in heating and so in effect, can be used in the air preheat application as well.
The use of an air conditioning system as a method of climate control within an AHU generally outweighs other methods such as gas and electric in both efficiency and cost of installation. It is also important as an alternative if the site in question has limited electrical supply. Power requirements of electric heater elements are demanding and in comparison, air conditioning has low start up currents, inverter control, and substantially better output to input energy ratio. The integrated heat pump systems that can be specified within AHUs are a good accessory, but such valuable energy saving functions as preheating a building before occupancy on a cold morning, without introducing cold fresh air, are limited. This is because both condenser and evaporator are mounted within the AHU air stream, limiting the recirculation aspect. External solutions can remove or add energy to the air stream because energy can be absorbed or rejected from outside the AHU via the outdoor unit.
VRF AHU single.
28 September 2019
www.acr-news.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56