What’s best? Should I use the existing ballasts or bypass/remove them?
This is an important question. While it is a simple question, the answer is not.
Separate of anything to do with the LED retrofit, all buildings with light fixtures using external ballasts face a large looming cost when these fail. Buildings can have many hundreds of such fixtures – in T8s in parking lots, and in wall and ceiling sconces. These ballasts typically last for many years, potentially over 10 years. When this looming cost will come up depends on when the building was built or when the ballasts were last replaced.
If the ballasts are replaced individually when they fail, it can be expected that the labour cost will be at least $100 each – the minimum time and call out travel cost of an electrician. The total looming cost can therefore run to many tens of thousands of dollars. It is quite likely that this cost has been overlooked and does not feature in buildings’ Depreciation Reports. So a budget for this may not be planned for in the building’s contingency fund.
This cost can be reduced very significantly by pre-emptively replacing the ballasts in batches, when there are signs that ballasts of a certain vintage are starting to fail with some frequency. The ballast replacement job may only take 10-15 minutes per fixture for an experienced electrician. So the cost savings can be greater than 75%.
These observations hold without anything to do with an LED retrofit. Why this issue arises when an LED retrofit is being considered is that this is an occasion when a batch process can address this looming cost of ballast replacements. But the economics needs to be very carefully considered, because the cost of involving an electrician at every fixture is not something that is needed for the LED retrofit where LED lamp technologies are used that work with the existing ballasts.
As noted in the FAQ Why does the standard Greenlight model avoid re-wiring fixtures wherever possible? in addition to the costs of having an electrician do work at every fixture, there are significant extra permit costs when the wiring of a fixture is touched. Also, if this wiring is more than just replacing the ballast – so if the ballast is bypassed or removed – a permit pulled by a FSR-certified electrician is needed no matter how few fixtures are involved.
There are also important efficiency and payback issues to be considered. One of the functions of ballasts is that they limit the current (power) going to the lamps, especially when more than one lamp is being driven off one ballast. For example, with T8 tube fixtures the power results with very common Philips brand ballasts are:
|Number of 4ft 32W T8 tubes per fixture with 1 ballast||1||2||3||4|
|Power draw of existing fixture, Watts||33.7 W||55.8 W||86.3 W||92.3 W|
|- per tube||33.7 W||27.9 W||28.8 W||23.1 W|
|Power draw of fixture with equivalent 15W LED tubes||14.1 W||25.3 W||36.2 W||36.3|
|- per tube||14.1 W||12.7 W||12.1 W||9.1 W|
|- Savings % of LED||58%||55%||58%||61%|
|Power draw with LED tubes on direct AC power||15.9 W||15.9 W||15.9 W||15.9 W|
|- Savings % of LED||53%||43%||45%||31%|
As can be seen by the % savings numbers, the LED operates more efficiently using the existing ballast than if replacing it. It is true that the LED on direct AC power will be brighter than with the ballast. However, the purpose of retrofits is to save energy. As long as the LED tubes on ballast are providing light levels that are adequately equivalent to the fluorescent tubes they replaced, the priority choice should be better energy savings, where this is economical.
This can be revealed in the economics. Taking the data for a 2 tube fixture (the most common), the watts saving on ballast is 15.3W; on direct AC power it is 12.0, so 3.3W less. If operated 24 hours per day the energy savings on ballast are 0.08 kWh per day better than on direct AC power. This is about 0.8 cents per day better. For a ballast costing about $20, this means it will be paid for in extra energy savings in about 6.8 years – so well within the life of the ballast.
One final technical factor is that in some situations the ballasts are needed to protect the fluorescent (or LED) lamps. This is particularly the case when the supply voltage is 347V AC. In such situations the ballasts need to remain in place for the LED retrofit.
Taking all the points above into consideration, Greenlight’s recommendations are:
- The LED retrofit should be undertaken in the most economical and affordable way possible, which is the use of LED technologies that work with the existing ballasts.
- If some ballasts need to be changed at the time of the retrofit, e.g. because they are of a type that is not compatible with the LED lamps, depending on the economics for the specific type of fixture, they can either be bypassed/removed or a new compatible type ballast installed. This specific work needs to be done by an electrician with the correct certifications, and permits if necessary, under the responsibility of Greenlight.
- To address the looming cost of when the existing ballasts eventually fail (which can be many years in the future), some of the energy and maintenance savings that the LED retrofit provides can be placed into the buildings Contingency Fund for an eventual batch process pre-emptive replacement of ballasts.