Letters

We need not be the dying breed

Climbing out of recession, we should take note of the hidden losses in manpower and ability. Many of the engineers lost from employment may not return to building services, preferring a more secure position rather than suffer the vagaries of the construction industry. Where are the new candidates going to come

from? In the last year, I have noted several opinions and letters in the Journal which bemoan the lack of suitable graduates or other candidates coming into the industry. My particular engineering degree course at the University of Strathclyde disappeared years ago, as have courses at Liverpool, Bath and many other institutions, due to lack of applications from undergraduates. Where would we be without the stalwart universities that have survived, and the new universities who appreciate our discipline? But I place the core problem earlier in the education process, at school stage, where mathematics and physics are dying subjects. In my view, you can’t be an engineer without an understanding of both these subjects, which makes this a major problem for our industry. There is also the problem of some of

our professionals moving over to low carbon and energy work. These are many of the aspiring engineers that we need in building services, but we are losing their analytical abilities to a peripheral aspect of our services. CIBSE is going down a path, in my view,

greater in many systems, this is not the case in all of them. The article quoted heat pumps with flow and

return temperatures of 50/45C, in which the flow rate would increase unless improvements of the building envelope reduced the heat losses by more than 50 per cent. It should also be noted that the heat that can be dissipated from the existing emitters, for example radiators, will be decreased due to reduction of the heat

the heat source is changed to, for example, a condensing boiler (55/35C), the temperature differential required for conversion will be reduced to 25C and the conversion factor of 0.406 needs to be used. This will result in the same radiator having output of 406W, which is around 64 per cent of reduction of the original capacity. Therefore, even with the improvements in building envelope – reducing the heat losses and infiltration – together with original oversizing of heat emitters, this might not have been as high as 64 per cent. It is also stated in the article that low flow rates mean less heat needs to be generated. The fact is that the amount of heat that requires to be generated does not depend on the flow rate but on the building heat demand together with system losses – these are the basics. Readers should also refer to CPD

article in the same edition (February, page 63), which discusses the design of air source heat pumps for heating and which confirm the above facts.

Michal Koscielniak, mechanical

engineer, SVM Glasgow

Is the recession driving engineers from building services, asks Ken McDougall, left. See also our jobs survey article, page 46.

where a more accurate description of the letters should be the Chartered Institution of Buildings, Sustainability and Energy. If we lose the ‘building services’, we will fail as a sector in construction and as a learned society. Now is the time to ensure our prosperity through education and through an industry which young people see as inspiring. Do building services engineers really need to be a dying breed?

Ken McDougall

The true basics of heating flow rates

Your article on commercial heating, ‘Back to basics’ (February, page 50), could be misleading. It states that usage of heat generators such as condensing boilers or heat pumps reduces flow rates. The fact is that although the temperature differential between flow and return will be

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CIBSE Journal May 2010

source temperature settings. The emitters are not as much sized for the delta T between flow and return, but for the delta T between average emitter temperature (which is effectively average of flow and return temperature) and the room temperature. For example, take an existing building with

a 82/71C heating system and analyse a sample radiator – Stelrad Elite K1 600mm high and 1,000mm long. Based on the manufacturer information, the heat output would be 1,000W at 75/65/20C; and to get actual output, a conversion factor needs to be used for temperature difference between average flow/return temperature and the assumed temperature within the heated space. For 82/71C system the temperature

differential would be around 55C (it is actually 56.5C), which gives a conversion factor of 1.132 and actual radiator output of 1132W. After

Use the green solutions

The government’s target of 3m greener, more affordable new homes by 2020 is commendable but there are millions of people who need a solution now. As an industry, we already have comprehensive technical

solutions to eradicate the situation where people have to choose between heating, eating and paying rent. It’s critical that we continue to promote next-generation cost-effective and energy efficient products to those in public – and private – housing, who can specify for change and a change for the better.

Neil Evans, general manager, Thermo-Floor

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Please send all letters and any other items for possible publication to: bcervi@cibsejournal.

com, or write to Bob Cervi, Editor, CIBSE Journal, Cambridge Publishers Ltd, 275 Newmarket Road, Cambridge, CB5 8JE, UK. We reserve the right to edit all letters. Please indicate how you wish your letter to be attributed, and whether you wish to have your contact details included.

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