First, I think it should be recognized that exergy analysis has been used thoroughly for evaluating the performance of equipment, processes and systems involved in buildings (e.g. heat exchanger, dehumidifier, boiler, etc.) for a number of years.

That being said, it is true that when referring to the overall building performance, most people think in terms of the 1st law, not the 2nd. If you consider the overall building as your control volume with its various flows in and out, exergy analysis might be relatively straightforward to apply, but might reveal little. On the other hand, looking at the different building components and systems could be insightful. Exergy analysis can also help to assess the environmental impacts of buildings. By the way, as far as I know, ASHRAE has a technical group focussing on exergy in buildings (http://tg1.ashraetcs.org/).

Finally, one of today’s “hot topics” that I would also link exergy with is life cycle analysis (LCA). I think it would be worthy to determine how exergy is destroyed not only in the operation of the building, but in the production and transport of building materials, during the construction phase, in the deconstruction, etc.

I hope this helps you.

Why should the entropy go into this consideration?

The second law of TD states that the entropy will never decrease in isolated systems (and hereby "isolated" means that there is no exchange of energy or matter with ist surroundings - that is impossible for buildings).

You may also say that the 2nd law states that heat will always go from a system with higher temperature to one with lower T and never the other way round (except you do some work on the systems).

So, how would you put the second law into the energy performance of a building? :)

Talking about second law of thermodynamics equals the consideration of exergetic efficiency. Since the quality of energy for a building is always straight forward; for heating and cooling based on the comfort temperature and for electricity, the amount of the consumed electricity is the exergy used. The building electrical and heating performance gives the whole information about the performance and no need for the second law (exergetic) efficiency, however considering exergetic efficiency gives a more thorough view about a building which inturn is more complicated to calculate.

First, I think it should be recognized that exergy analysis has been used thoroughly for evaluating the performance of equipment, processes and systems involved in buildings (e.g. heat exchanger, dehumidifier, boiler, etc.) for a number of years.

That being said, it is true that when referring to the overall building performance, most people think in terms of the 1st law, not the 2nd. If you consider the overall building as your control volume with its various flows in and out, exergy analysis might be relatively straightforward to apply, but might reveal little. On the other hand, looking at the different building components and systems could be insightful. Exergy analysis can also help to assess the environmental impacts of buildings. By the way, as far as I know, ASHRAE has a technical group focussing on exergy in buildings (http://tg1.ashraetcs.org/).

Finally, one of today’s “hot topics” that I would also link exergy with is life cycle analysis (LCA). I think it would be worthy to determine how exergy is destroyed not only in the operation of the building, but in the production and transport of building materials, during the construction phase, in the deconstruction, etc.

I hope this helps you.

When you talk about energy it takes first law into consideration which only looks at quantity of potentials. But, exergy analysis is a tool for bringing quality of potentials into study aswell which employes entropy generation concept. So, it is not correct to say "why energy efficiency doesnt consider second law" cuz basically it should not. Anyways, for building related components exergy anakysis tool can be used but u should note that the reference environment definition for components varry according to their place; inside or outside. 

The exergy entering a building (with rare exceptions) is typically completely lost since the heat emanating from it is always on the environment level and thus carrying no more exergy.

On the other hand exergy analysis is mostly sensible if processes are analysed. The "performance of a building" is not a typical process, though. The question would get a practical meaning, though, if the energy provision to the building is scrutinized - like comparing a conventional furnace heating to a heat pump system. But such questions do not address the building by itself.

Hi Petra

Can you please make it more clear for me. I have seen papers regarding building stuff using second law. Basically I dont know what does this question address.

Thank you

@Reza Soltani,

if you consider heating systems as "building stuff" you are already there. Exergetic (or entropic) performance will address the quality of energy utilization, but may be somewhat misleading: E.g., if you take different carburants for a conventional fossil heating system, you will end up at different entropic/exergetic efficiencies. But if obtaining the "better" carburant involves some extensive provisioning the exergetic/entropic balance may be completely reverted. Following this road you will end up in lca (life cycle assessment) considerations (here: for the heating process), but this is not the scope the "building performance" is addressing first place, IMHO.

My point of view is the same @Louis Gosselin and others of you.

I believe that the quantification of exergy destroyed is closely related to the environmental impact of an energy source. The choice of a quality of an energy sources similar to the quality necessary for internal wellness in a building, is necessary. To date, the energy performance is used to quantify the "sustainability" of a building or not, this means that it has an"environmental" value. I do not see why the second law should not become a part of an overall assessment of the impact energy.

@M.G. Baldi: In general I share your thoughts, but once again the question: Where to define the balancing borders if you try to aim at the building and not a generalized life cycle analysis? Just an example: In a very well heat-isolated building it may be more wise from purely economic reasoning to provide heat just by a simple ohmic dissipation (which is presumably the worst case for exergetic considerations), instead of, say, a combustion engine that drives a heat pump. (I leave out renewable resources for now just to clarify my point of of the general valuation of exergy analysis for a secluded area of balancing.)

If you set your system boundary just at the building walls, the exergy result is clear. Only when you include additional resources involved (like the production of the elaborate heat pump, engine, hot water piping, etc.) in spite of very low absolute consumptions IN the house the contradiction w/r/to exergy analysis resolves. But it is then no more a question of a balancing of the building but a rather large and environment dependent system instead. Just put the identical building to Sibiria and to a rather warm surrounding, and you obtain rather different results.

Due to this effect I consider the exergy analysis result not as a describing property of the house but of the larger system it is interacting with.

Hi all

@ Petra, thanks, I fully understood when I look at your and Luois's comments. The matter is where to define your control volumes. naturally, based on dead state selection, if you choose building overall walls as your CV, then no exergy, though. 

But, how? how can we study a buidling with inputs and outputs without considering systems inside? Lets say there is building with only one component which is for instance a heat pump, what are the inputs and outputs then? Considder evaporator outside in ambient air and condenser and compressor inside. I would appreciate your help.

Regards

Reza

@ Marta, your question statement is not clear for me: it says why "energy" performance definition of a building is based on 1st law and not second law, I wrote the same in previous comments. 

I can see that you already have a paper entitled thermal exergy analysis of a building, is, so I can guess that your control volume is not building walls, is it? Thanks indeed

Regards

Reza

Thanks for the discussion @Petra Roosen.

In model of exergy analysis, the building is an transient open system  and his boundaries are a infinitesimal membrane, it is external of building walls. The external environment, the surroundings in model, are defined by the characteristics of air, water and land surrounding. The reference system changes if I shift the real place, and with the same characteristics of the system and the type of the solutions adopted to obtain them, of course, the exergy destroyed will be slightly different, but it is thermodynamically correct.

@Reza , thank you for the question.

Yes, I wanted to move the attention in "buildings"sector , we refer only to the 1 Law of Thermodinamics from the Thermodinamic point of view..

In model of exergy analysis, the building is an transient open system and his boundaries are a infinitesimal membrane, it is external of building walls. 

Thanks Marta

@Marta: "I wanted to move the attention in "buildings"sector , we refer only to the 1 Law of Thermodinamics from the Thermodinamic point of view."

If we only discuss matters of energy: Yes. If we look at the cost of energy consumptions (well aware of the different kinds of energy with their differing costs!) the point of view changes towards entropic effort, even if this point of view is - of course - somewhat noisy. You may even take the (exergetic) effort to produce respective energy converters (like heat pumps) into this perspective as well. To make my point for a more simple comparison, just compare costs for the kW electricity and heat. The different exergy of respective same *energy* streams is, in a certain way, represented by market prices.

Hi All,

Interesting discussion so far and thank to share your ideas.  In a real analyses of a buildings you need to first exploits the first law of thermodynamic which can assists you with the value of heating, cooling and electricity and other commodities. According to what Reza was trying to address, of course in order to improve the devices used in the systems for the thermal comfort we should take exergy analysis into our consideration. There was a chapter in ASHRAE titled (Exergy Analysis for Sustainable Buildings by I. Dincer) which fully address the importance of exergy analysis and recently researchers are trying to add exergy analysis in their commercial software. I know that Thermoflow for analyses of power generation units and ASPEN for process simulation have added into their software. I had a discussion with some professors from Concordia University and they were working on a proposal for Energyplus and Trnsys software so we can benefit from the second law of thermodynamic.  Besides, optimization of the building envelope is another important concept that should be fully covered as it directly affect the energy consumption of the buildings. There is a lack of optimization and even LCA for residential buildings as commercial software are working based on the inputs date however when you are planning to optimize such a building, you should either change the inputs or predict the optimization. One method is to use Response Surface Approximation Model (RSA) and use optimization algorithms. I would like to ask you to see the following papers regarding the exergy analysis for some buildings.

Ng Cheng Hin, J., and Zmeureanu, R., (2014) Optimization of a residential solar combisystem for minimum life cycle cost, energy use and exergy destroyed. Solar Energy 100, 102-113.

El shenawy, A., and Zmeureanu, R., (2013) Exergy-based index for assessing the building sustainability. Building and Environment 60, 202-210.

Zmeureanu, R. and Wu, X.Y., (2006) Energy and exergy performance of residential heating systems with separate mechanical ventilation system. Energy, The International Journal 32(3), 187-195.

@Pouria , thank you for your answer. Also my research is a combination of energy-exergy analysis to analyze the thermodynamic interaction between building and environment. I think that, before someone tries to add exergy analysis in their commercial software, it is necessary more research. My approach is different comparison a traditional exergy analysis of energy chain.

Thank you for papers suggested, i know 2 of these, yhe second one i don't think that i read it.

Marta, i am not a great specialist, but i think that today the performance of a building remains a question of heat exchange, mainly with outside and the first law is sufficient for this. The second law maters when other energies than thermal one, notably mechanical or electrical,  must been taken in account in great quantities. In a building there are commonly little mechanical or electrical devices of which energy amounts are small comparatively to these for heating or cooling the building, and even those amounts generally become heat inside the building and finally are included in  the main concern, which is the efficiency of the thermal insulation with outside. The case where the second law seems to be necessarly used is, as Petra Roosen says, if heat pumps are installed to improve the energy balance of the building, but it remains rare.

Entropy: A concept that is not a physical quantity

https://www.researchgate.net/publication/230554936_Entropy_A_concept_that_is_not_a_physical_quantity

Unfortunately I m not agree with your paper @Shufeng Zhang, there are many inconsistent aspects according to me. Anyway, thank you to answer, but honestly I prefer a discursive answer. Thank you.

@ Marta Giulia Baldi

Dear Ms Marta,

from my humble experience in energy performance , the exergy concept is used to asses the maximal work that could be produced from a source at a temperature higher than the ambient temperature . It is useful in industry processes or energy systems .However, in building streams or sources have a low value of exergy and no practical applications could be applied to transform this energy to work. It all depends on the context and the objective you are looking about.

Following