Commissioning of HVAC Systems

Presented at 17th world Energy Congress 1994, Atlanta, GA USA

by Klaus Schiess P.E., CEM

Presented in 1994, published in 1995 but still valid TODAY


In recent years various presentation and discussions have taken place which looked at commissioning as a separate process that had to be specified and implemented by a specialized entity in a project. This presentation discusses commissioning in the HVAC field and looks at it from an international perspective. The author has worked in Europe, South Africa (British system) and in the USA. The differences are discussed between the British and the American methods with some examples where the American way of commissioning was unsuccessful. The conclusion is that it is the design engineer’s job to test and accept (commission) an installation after the contractor has demonstrated the performance to the satisfaction of the design engineer. Once the plant is commissioned, it is put into service.


Commissioning is the process to verify that an installation performs as designed and specified. The installation is then officially put into service and becomes the property of the owner. It is like handing over the car keys with a handshake to the buyer and wishing luck when the proud owner drives it out of the sales lot.

For me this is one of the highlights in an engineer’s career: Here is the plant, it performs the way I have designed it. Individual thought and creativity becomes reality. That is what engineers do. They create machinery that is designed to satisfy certain requirements for the good of society. I have worked as an engineer on three continents and this gives me the opportunity to compare the different ways of constructing projects. Unfortunately, I find that in America it is the most difficult to reach professional satisfaction because in general, the engineer’s role has been relegated to produce a set of bidding documents after which the Contractor takes over.

During my time as a partner in a South African consulting firm we were asked by a large local contractor to redesign the complete mechanical and electrical services for a Holiday Inn project to be built in Lesotho. We were given the drawings of a well known American consulting firm which showed the design as if this Holiday Inn was to be built in America. We quite embarrassingly approached the US consultant if this was in order as they had totally ignored the fact of local conditions, available material and equipment, codes and the 380/220 volts and 50 Hertz, etc. etc. To our biggest surprise, they were perfectly happy, feeling they had done their job and were pleased that it would be done right. From our point of view, we could not understand how a professional firm could feel happy about having their totally useless design redone at client’s extra cost without blinking an eye. Today after working here for over 16 years, I understand.


In the British system the design team consists of an Architect, a Quantity Surveyor and the various consulting engineers: structural, electrical and mechanical. Sewerage and roof drainage is considered Architects work, while domestic water belongs to the field of mechanical engineering. The fee for each professional service is paid according to a percentage based on the final contract price of the project governed by rules of professional associations. For American standards, this would mean for example, the A.I.A. would determine the fee structure of architects, based on a sliding curve; the smaller the project, the larger the percentage fee. Fee undercutting is considered unethical. The paradox always exists, the more work you put into the project to save money, the smaller your fees. But to produce a good project at lowest cost is part of your competitive edge and gives you a reputation.

For American standards that would reek of price fixing, but it is definitely fairer to all design professions. The Architect is a colleague who is the leader by way of coordinating the various services falling under the Architects scope of work. The Architect’s fees include for this coordination work.

In the American system the Architect is boss and the engineers are paid by the Architect. This is equivalent to the captain of a football team getting paid all and being in charge of compensating the other players. I have been forced to negotiate my fees with an Architect who wanted the same amount of fees for coordinating than I as the mechanical engineer get for designing the mechanical system. I find it unprofessional that Architects can shop around amongst colleague professions and base their choice upon their largest profit. In the British system the Quantity Surveyor (QS) produces a Bill of Quantities which defines all structural and architectural quantities as read off the drawings. The contractor is asked to fill out unit prices for all materials and labor as specified. This is very useful and the hassles of change orders are greatly reduced. The contractor (or builder) gets paid only what was actually built as measured by the QS.

Electrical and mechanical contracts are performed by so called Nominated Subcontractors. The bill of quantities states that certain subcontracts with this estimated cost will be appointed as subcontractors nominated by the Architect following the recommendation of the consulting engineer with the clients’ approval. The subcontractors are determined by separate tender(bids) and the evaluation by the consultants. The main contractor has the right to refuse to work with a specific sub-contractor if valid reasons can be presented. The builder (contractor) gets so called 5% builders discount of the subcontractors’ contract price as compensation to coordinate the services of the various sub-contractors.

This demonstrates that with this system the engineers are in a much stronger position since the general contractor has no way of profiting from the subcontractors. I was shocked to see the power of the contractors in the USA. The contractor can still wheel and deal with different subcontractors even after the contract has been awarded.


Supervision is always part of the consultants job. This means attending site meetings which on larger projects could occur on a regular weekly basis. Such close contact with the project ensures early detection and confrontation with anything that is not according to specification. Commissioning is the main element and the crowning of supervision. The specification requires for the sub-contractor to demonstrate to the consultant that everything functions and performs according to specification. Air quantities and flow quantities are checked, control sequences demonstrated and performances checked. False alarms are simulated and fire dampers are dropped to ensure their functioning.

Once everything is checked and found to be to the satisfaction of the engineer, the plant is handed over to the owner. When the plant has been used before commissioning took place then there are usually some disputes about the date of beneficial occupation or when the guarantee period starts. Often especially with HVAC projects, the consulting engineer may  have to be available for a year to assist with teething problems. It often takes operating through all four seasons before all bugs are ironed out.

The engineer who designed the project is the best person to know whether the plant was built according to specification or not. The frequent attendances during the building process allows close scrutiny of the subcontractor’s work. Having checked and accepted the performance of the system the engineer obtains the knowledge that the system works as designed. It also allows the engineer the confidence to know that any query the owner or operators may have can be answered with the knowledge that the fault is not with the design.

The process of being so closely involved with the project during the construction stage and the commissioning phase also gives the engineer the practical experience and feedback from the construction site that is so essential to becoming a good engineer.


When I came to America, my first employment was as HVAC engineer in the mechanical department of a large architectural firm. My personal impressions and opinions that I have since developed are meant as constructive suggestions.

The first thing I was told, was that consulting engineers do not supervise. Only site observation is done. I soon learned about the subtle difference – responsibility. And then soon followed the discovery of one of the most paralyzing agents in this wonderful country: Lawyers and lawsuits.

As contractors take responsibility, they become kings. The consulting engineers work is often reduced to preparing drawings as a base for bidding. After the contract is awarded, the contractor then starts to offer “savings” to the client and things get changed. Sometimes it is nearly necessary to add a disclaimer, just like Hollywood movies have to do: “Any similarity of the final installation with the original design is purely coincidental.”


A typical example of the contractor’s power was the experience with my first thermal energy storage project (TES) after moving to San Diego. The client and architect were very well disposed towards the idea of a TES system. With an incentive rebate from the utility company, the client decided to design the building with a TES system. The contractor who was already appointed tried everything to convince the client and the architect that this was an expensive solution. The contractor then offered to do the design for a heat pump system for free. All this because the contractor was reluctant to try something new and worries about profit margins when building an unfamiliar system. By the way, is there ever such a thing as getting the design for free? The client resisted the temptation to “save money” and one of the first TES system in San Diego got built. Guess what? Soon after the contractor solicited work as a TES expert.


In America, commissioning is then mainly the contractors problem. Most of the time it falls into the lap of the controls contractor. A specialist is called in for a balance report with the accent on report which often becomes an exercise in typing. Copy the cfms given on the drawings onto the report and vary the “measured” cfm by 1% or 2% and the report is done. Actually, I have seen worse. Exact copies of the cfm specified.

Practical experience soon shows that when it comes to paying certificates; the last 5% usually take half the time to complete. By the time commissioning stage arrives, all the money is paid, the retention is not worth much, so the idea is to get off the job site as fast as possible or as fast as guarding the reputation allows.

Commissioning is most important but occurs at the worst time.

Illustrative examples on commissioning:

Chilled water systems:

One of my first assignments with my first US employer was to design HVAC alterations for a building which formed part of a central chilled water plant. I wanted to go and see the conditions and parameters of the existing system. My superior expressed that this was a waste of time because our scope of work was for the building only. Well, I went anyway and discovered a beautiful plant room, immaculately kept clean.

I checked the supply and the return system pressures as that was the main reason for my coming to see it. The pressure range was somewhere 60 down to 45 psi which looked fine. But then I discovered that the pumps were pushing 120 psi. Now this was a big system with three 300 HP pumps. I started to look for the missing 60 psi. It did not take long to discover three cranked valves between the pumps and the system. Upon asking the operator, I was told that from the beginning they had tremendous problems and two years prior they had called in a balancing specialist. Well, guess what? They “balanced” the system as best they could by cranking main isolating valves.

These balancing experts must have known that they treated the symptom but did not address the cause. Were they scared of the original designer to clearly state that the installed pumps were way out of range? There was this plant destroying about 300 HP across those cranked valves continuously for 24 hours every day, but the firm prided itself for being energy efficient with the little red signs, “turn off the lights when leaving the room”. Does anyone believe this plant was commissioned? Did the balancing experts fear the wrath of the designer if they exposed the wrong pump selection?

Owners remember whenever there is an addition to an existing system, consultant and contractor tend to have tunnel vision and consider only what concerns them directly. But the owner has to realize the effects on the total system.

Examples of commissioning that probably did not happen:

Air supply to ringfeed:

It is customary in spec office building design to provide the shell and with it, the basic central variable air volume (VAV) supply with a ringfeed duct on every floor. Tenant improvements will then later connect the VAV boxes to the supply according to tenants individual needs.

Commissioning is practically impossible under these circumstances. Split responsibility is introduced and too many variables muddy the waters. There may even be different contractors doing tenant improvements with everybody in a rush to finish. The combined effects of variables such as static pressure, friction drop from main to VAV box and downstream of the VAV box, supply air temperature, peak cooling capacity, initial low load because of partial occupation, all really only show up one to two years later when the building is fully occupied and reaches peak conditions.

Laboratory Exhaust

Recently it was discovered that three exhaust fans were running backwards for three years before the static pressure problems could be eliminated in a laboratory. Do you think the air balance report had any value on that project?

Commissioning of Museum Library:

I was involved in an energy audit for a Museum Library which contained old and very valuable books. The library was protected by very sophisticated HVAC controls and a Halon fire protection system with an evacuation system. I found a 3,000 cfm exhaust fan operating continuously. The maintenance personnel and the automatic control operator and even the fire chief did not know what fan I was talking about. It turned out to be the Halon exhaust fan which had been running for years without anybody knowing that fan was even there because it had no switch or circuit breaker. How much energy was lost by exhausting conditioned air all these years and what if a fire had occurred? The fan would have exhausted the Halon and helped the fire by neutralizing the halon system.

Basic Approach to Commissioning

It is tempting for the contractor to expect that the controls contractor will get things working. Often the Energy Management and Control System (EMCS) becomes the solution to all commissioning problems. There is no such thing as a magic black box that gets things going. The control sequence is what the engineer puts in and it is the engineer who should be satisfied that the control contract performs to the engineer’s specification.

This especially applies to TES systems where control sequences must be simple so that the person on the floor, the operator and maintenance people understand the system. If things get too complicated controls will become manual.

A worthwhile slogan to remember:

Any automatic control will revert to the level of competence of the operator.

The contractor should not be the only party to pass the final test. It is like correcting your own exam paper.

The contractor must do an “in-house” commissioning with all the subcontractors and parties involved. The commissioning of the engineer is then the exam to demonstrate how well the plant functions. The engineer then commissions (put into service) the system by checking through every function and control sequence or cycle to ensure that everything functions as designed and specified.

Contractors think commissioning is like a structure. Once it is built you can walk away from it and it will live forever or at least for the next twelve months, the guarantee period.

Mechanical systems are different. They are like living things with moving parts that can vibrate, make noise, burn out etc. So it is for the engineer to be ingenious and see their own original thought become reality.

Unfortunately even the most idealistic engineer has to make a living and they have to be paid for their work. Therefore, in the contract with the client the engineer should be paid for the services of observation and “commissioning” the system. The engineer then specifies that the contractor must allow in the cost a demonstration of the system performing to the engineer’s satisfaction.

During the commissioning process the engineer even with the full knowledge of the design must become somehow detached and look at it unbiased and with no preconceived ideas. Nothing must be assumed. Everything must be checked out. An arrow on a pipe means that the person who painted the arrow thinks the water flows that way. I have seen a chilled water system where a check valve which was installed the wrong way caused a lot of problems for weeks. It was a student who found the mistake. He followed the system flow from first principles and asked innocently whether the arrow on the check valve indicated the direction of flow.


Commissioning, in spite of the threat of lawyers, should be the culmination of the project for the engineer. Like shaking the hand of the client and wishing him well when driving out the new car. I feel somewhat robbed if I was not totally involved with a project to the end. I want to see it work and want to have the knowledge that my design is good. That makes me proud to be an engineer.

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