Before you can evaluate performance, you need to identify big-picture goals for the institution, followed by objectives that structure the goals into measurable objectives.
I doubt that all libraries have identical goals and objectives, so it is hard to generalize.
Right now I am working on library social responsibility. So far I have learned that library performance is usualy measured tbrouhg service quality, maybe you can try that way. It definitely has nothing to do with commerce.
It is a sci library issue since a sci library is , by definition , a non-profit organization, and its performance cannot be measured by a regular market value of "investment/profit", so the evaluation of sci libraries considers usage and effectiveness of library material which need scientific tools to measure.
The present era is the inter-disciplinary era, where one's knowledge is not restricted to one particular field of knowledge. Being a Library Science student, I can collaborate with any other discipline giving rise to inter-disciplinary works. So, I would say that the question asked here could be related to both fields, we cannot confine it to just one of the two.
Performance of Library can be measure through its value added services if you provide quality service to your library patron than library performance is rated positive value. As mentioned by @Avishag Gordon it not a profit taking or investment return organization.
@Huma Shafiq link in both thought I sum up in Knowledge economy (client) patron are very important s/he will judge your service and collections his feedback able to you achieve your desired goal. Quality assurance tools i.e ISO-9001, 9002 also set a paradigm for your library standard and quality rather than managing monetary,commerce or economy value of your library. You can further elebrate your library quality in following articles
Sossamma, G., Pauziaah, M., & Kiran, K. (2002). In pursuit of quality-towards MS ISO 9001: 2000: The experience of the University of Malaya Library. Kekal Abadi, 21(2), 1-6.
Read ranganathan, mine existing data, contact statisticians, interview clients, contact economists, read library literature, create a model, insert local data, etc. then get many libraries to run the model. Then send it out for review.
There are several issues that scientist look at in evaluating performance of libraries. Some focus on service quality (you can read on LIBQual), user satisfaction, user loyalty among others. These indicators try to list some performance indicators (library personnel performance, library environment, library resources and collections etc.). I recommend you read the LibQual survey tool and you may be well informed.
An excellent article about key Performance Indicators of Library !
" Libraries across all sectors serve a particular purpose and set out to achieve the goals and objectives of the library’s stakeholders. These objectives will differ according to the nature and strategic function of the library and the expectations of its user community. If the library achieves its aims or goals, there is a high likelihood that the library’s users and the communities it serves will consider it valuable (financially or otherwise). Managing objectives strategically, then, allows libraries to achieve its desired outcomes and those of its users. Library stakeholders and customers also expect to receive high-quality service, and libraries now exist in a culture of striving to achieve excellence and deliver continual high-service performance.
“Service excellence is not necessarily achieved using traditional quality assurance processes but that it is more likely to be attained through strategic planning processes aligned with key performance indicators that provide accountability” (Holmes & Parsons, 2016, p. 25)..."