When buying, installing and Commissioning a chiller, close attention should be paid to the terms and conditions of sale and warranty on the manufacturers order.
1 – Installation of the necessary items for Commissioning and maintenance
Every chiller I see has different combinations of valves, filtration, BMS points and measuring points. This really effects the ability to test, Commission and maintain the chiller and CHW system. Many installations are missing necessary items, mainly due to ignorance or value engineering with weak engineers not taking a stand for their design. There is no agreed, good practice in the building services industry.
2 – Strainer installation to meet the warranty requirements
If you read the small print from the chiller supplier there is a requirement for a strainer to be installed on the inlet of the evaporator for each chiller. If this is missing the warranty is void. I have been involved in a project where this actually happened and the owner had to replace, at their cost, a failed chiller when it should have been covered under warranty. For the North American design engineers out there (this is a much smaller issue in the UK), a strainer on the chilled water pump does not cut it. There should be a strainer on each main chilled water pump and on the inlet to each chiller evaporator.
3 – Actual commencement of chiller warranty
Again read the small print. Warranty from the suppler commences from the date the suppliers technician starts up and sets the chiller to work. This date can be months prior to substantial completion when contactually the warranty should commence for the owner. This disconnect can result in the owner not getting the warranty that has been contracted. Again I have been involved in the past with a clients claim against a contractor for inadequate warranty.
What to do? IMHO:
- Agree at design phase with the owner design team and Commissioning Authority, a chiller detail that includes the necessary items required for Commissioning and facilities maintenance.
- Install a medium mesh strainer on the inlet of each chiller evaporator. It really is not a lot of money in the big picture!
- Ensure the chiller warranty commences at substantial / practical completion.
I have attached below a suggested chiller detail that is optimized for Commissioning and Facilities Management. This is a whole life perspective not a first cost perspective. When reviewing remember we operate in an industry where there is little agreement on good practice, valve location, valve authority, number and location of test points and flushing methodologies. This detail is what I would like to see to enable effective commissioning and diagnostic testing. Yes, chiller salesman will tell you their chiller has “internal controls and routines” that enable chiller Commissioning, safeties and optimization. However they, IMHO, should be supplemental to the items on my detail. My notes on the detail are;
- A flushing by-pass is required to protect the chiller from aggressive chemicals during flushing. During installation and flushing the chiller should be isolated and the evaporator pipework capped/shut off for protection from debris and poor site “house keeping”. On completion of flushing, the chiller evaporator should be back flushed prior to connection to the chilled water system.
- A maintenance by-pass is required, particularly in mission critical systems. The flushing by-pass can double up for this function.
- Pressure connection points to measure the pressure drop across the strainer, evaporator and motorized isolation valve cost very little but provide a life time of commissioning and diagnostic use.
- Temperature gauges are for quick diagnostics but should not be considered accurate. They should be installed so that they can be read easily (without obstruction or ladders) with the correct range for the system application.
- Insulation should be vapour sealed but allow access to pressure connection points and commissioning valves without the need to cut and reinstall insulation.
- Commissioning valves to be installed with 10 straight pipe diameters upstream and 5 straight pipe diameters down stream to ensure optimum performance.
- Isolating valves to be high performance butterfly valves. These valve types provide rapid isolations i.e. 90 degree movement to close plus there is an instant visual verification that the valve is open or shut. Important for mission critical applications.
- Install paddle flow switch for proof of flow to controls system. Do not use a differential pressure switch at the pump for proof of flow. With isolating valves fully shut, a differential pressure switch will give a false proof of flow signal. A paddle switch senses flow not pressure and is therefore accurate and more reliable. Important for mission critical applications.
- Install commissioning valves and pressure test points with connection points face up or on a vertical plane to prevent dirt collection issues.
- Evaporator pressure drop and flow rate to be measured and recorded in the commissioning report with the system balanced.
- Motorized isolating valve (if installed) pressure drop to be measured and recorded in the commissioning report with the system balanced.
- Clean strainer pressure drop to be measured and recorded in the commissioning report with the system balanced.
- Confirm paddle switch and motorized isolating valve (if installed) operation and consequential alarms back to BMS head end.
- Chiller flow switch enable and emergency chiller shut down to be tested.
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