RECD Upgrades During a Factory Expansion: What Should Be Reassessed?

A factory expansion is planned around new lines, floor space and shifts. Power backup gets attention when someone notices the generators will not cover the new load, and the Retrofit Emission Control Devices (RECDs) on those generators get attention even later, often when the pollution control board asks a question nobody can answer.

That order is backwards. An RECD is selected for a specific engine, exhaust flow, back-pressure budget and duty, and an expansion can shift several of those at once.

This RECD factory expansion checklist covers ten things that change when a factory grows, each with what to check and what to do, followed by an illustrative worked example with the arithmetic shown.

Why expansion is a natural review point

Most RECD reviews are triggered by one event, such as an overhaul or a failed test. An expansion bundles many triggers together: the electrical team changes the load, the civil team changes the building, the EHS team changes the consent and operations changes the shift pattern. Treating it as one structured review keeps costs down (exhaust and cable changes are cheapest while the walls are open), reduces surprises at SPCB inspection and lets you capture a baseline before anything changes.

The 10 things that change when a factory grows

1. The total load grows, and new sets arrive

What changes. Maximum demand during a grid outage rises, which usually means adding a set, upsizing one, or both.

What to check.

• The new maximum demand in kW, not just connected load. Use metered data from the existing plant and a reasoned estimate for the new block.
• Each set’s rating in kVA and kW, and the expected power factor. See how to read generator kVA and kW ratings.

What to do. Write down, for every set, the expected kW at peak, at a typical shift and at the lowest-load shift. Every new set needs its own CPCB type-approved RECD selected for that engine.

2. The duty changes, often from standby towards prime

What changes. If the grid connection lags behind the expansion, the DG sets run far more. A standby system at 200 to 300 hours a year can drift towards 1,000 hours or more, which looks like prime duty.

What to check.

• Run hours per set for the last 12 months, and a realistic forecast for the next 12.
• Whether the sets will run during planned peak-tariff periods, during grid curtailments or only during outages.

What to do. Treat a duty change as a specification change. Read prime power vs standby: can the same RECD specification apply? and ask your supplier whether the existing device and its maintenance plan suit the new hours. More hours means more soot and ash, so cleaning intervals may need to shorten.

3. Existing RECD sizing may no longer match the new load pattern

What changes. A bigger factory does not automatically make each existing RECD “too small”. An RECD is sized to the engine’s exhaust flow at rated output; if the engine is unchanged, so is the maximum flow. What changes is where the engine spends its time.

What to check.

• Whether any set will now spend long periods at low load (for example, three sets sharing a light night-shift load), which lowers exhaust temperature and can affect passive regeneration.
• Whether any set will be pushed close to 100% for long periods during contingencies.

What to do. Compare per-set load before and after, not total load. If the per-set load drops sharply, read choosing an RECD for a generator running at low load and look at your start-stop logic. The technical background on DPF regeneration at DieselNet explains why exhaust temperature matters so much for filter-type devices.

4. Back-pressure margins shrink

What changes. Expansions often lengthen exhaust routes: a DG room moves, or a stack must rise above a new roof. Extra pipe and bends add back-pressure on top of the RECD and silencer.

What to check.

• The engine manufacturer’s maximum allowable exhaust back-pressure.
• The measured back-pressure at full load today, with the RECD in a clean or known condition.
• The added back-pressure from the new route, and the rise in RECD differential pressure between cleanings, which eats into the margin as soot builds.

What to do. Build a simple back-pressure budget for each affected set: existing measured value, plus new route, plus an allowance for loading between cleanings, against the OEM limit. If the margin is thin, the fix is usually a larger pipe diameter, fewer bends or a shorter route, decided before the civil works lock it in. See how exhaust back-pressure affects a DG set.

5. The exhaust route and the building around it change

What changes. New mezzanines, cable trays, roofs and relocated DG rooms crowd the exhaust. A stack may end up near a new fresh-air intake, and a once-accessible route may sit behind a mezzanine column.

What to check.

• Clearances from the RECD and hot pipework to new structures, cable trays and combustible materials.
• Maintenance access: can the RECD still be opened, cleaned and inspected, and can a filter or cartridge be removed and lifted out?
• Supports: will new vibration or roof penetrations load the exhaust unexpectedly?
• Stack height and discharge location relative to the new building envelope and the consent conditions.

What to do. Ask for an updated general arrangement drawing that shows the RECD, supports, access zones and stack, overlaid on the expansion layout. Use what to include in an RECD general arrangement drawing as a template. Mark maintenance zones on the architect’s drawings as “keep clear”, so they do not get filled with racking six months later.

6. The consent and SPCB records stop describing the site

What changes. Your consents and DG registration describe the generators on site. Adding a set, changing capacity or moving a DG room usually needs an amendment or fresh application. Processes differ by state, and in Delhi NCR the Graded Response Action Plan (GRAP) adds operating restrictions during poor air quality.

What to check.

• What your current consent says about the number, rating and location of DG sets and their emission control.
• Whether your SPCB treats the expansion as an amendment, a fresh consent or a capacity expansion requiring a new application.
• Whether the new set will be compliant from its first run, including during commissioning.

What to do. Talk to your consultant or the SPCB early, ideally while the expansion is still on drawings. See how to get a pollution NOC for a DG set, and check current national guidance on the CPCB website. Keep copies of the RECD type-approval certificates for every set, old and new, ready to submit. Do not plan to run a new set without its RECD “temporarily” while paperwork catches up; that is a compliance risk, and any interim arrangement should be agreed with the SPCB and your supplier in writing.

7. Monitoring and BMS integration need to grow too

What changes. A new set means another RECD controller, more sensors and more alarms. If a building management system (BMS) arrives with the expansion, RECD data may move to a central screen for the first time.

What to check.

• Which RECD parameters (differential pressure, exhaust temperature, fault status) are monitored today, and whether the new controller provides the same. If your RECD controller offers a communication port, confirm the protocol, register map and units before the BMS integrator writes any code.
• Alarm routing: who gets which alarm, on which shift, after the expansion.
• Power supply for monitoring during an outage, because the generators run precisely when the grid is down.

What to do. Write one monitoring specification that covers all sets, old and new, and give it to both the RECD supplier and the BMS integrator. See integrating RECD monitoring with a building management system. Where you have Modbus links, the published Modbus specifications are the neutral reference for both parties.

8. Testing obligations and retest triggers multiply

What changes. The new set needs commissioning and acceptance tests for its RECD. The existing sets may also need retesting if their engines, exhaust routes or duty have changed materially.

What to check.

• Which changes on each existing set count as a retest trigger under your consent, your supplier’s warranty terms and your own internal standards.
• Whether “before” readings exist for existing sets so that “after” readings mean something.

What to do. Use when to retest an RECD after DG set changes to classify each change. Record a baseline for every existing set before any exhaust modification: load, exhaust temperature, back-pressure and RECD differential pressure at a stated load and warm-up time. Then repeat the same readings at the same conditions after the change.

9. Budget and phasing decide what happens first

What changes. Emission control is an easy line item to trim, but modifying an exhaust after the building is finished means scaffolding, shutdowns and rework.

What to check.

• RECD supply and installation for the new set.
• Exhaust modifications on existing sets, plus sensor relocation and cabling.
• Testing, consent fees, and a contingency for back-pressure fixes.

What to do. Put the RECD work into the expansion’s capital budget as its own package, with a named owner. Phase it so that the new set never runs without its device, and existing sets are modified during planned outages, not during production peaks.

10. The sequence must fit expansion construction

What changes. RECD work depends on several construction steps. Miss them and the generators are commissioned late or modified twice.

What to check.

• When the new DG room and stack penetrations are ready.
• When the existing sets can be taken out of service, and what covers the load while they are down.
• When the consent amendment is expected, relative to the planned first run of the new set.

What to do. Add the RECD milestones to the master construction programme, not a separate spreadsheet. Plan backup cover during modifications using the approach in preserving backup power during an RECD retrofit.

Worked example (illustrative): from 2 × 500 kVA to 2 × 500 kVA + 1 × 1,010 kVA

The numbers below are illustrative. They are chosen to show the method, not to describe a real site or a specific product. Use your own metered data, OEM figures and supplier advice.

The starting point

An auto-component plant near Gurugram has two 500 kVA DG sets (Set A and Set B), each fitted with an RECD. They run synchronised on a common bus. At a power factor of 0.8, each set is rated at 400 kW, so the pair has 800 kW of capacity.

The plant’s maximum demand during an outage is 650 kW. The sets run as standby, about 250 hours a year each, mostly during summer grid outages.

The plant is adding a second production hall and a new shift. Maximum demand will rise to 1,300 kW. The plan is to add one 1,010 kVA set (Set C), rated at 808 kW at 0.8 power factor, to the same synchronised bus. The existing DG room is too small, so Set C will sit in a new DG room at the end of the new hall, and the exhaust from Sets A and B will be rerouted because the new hall’s roof blocks the old stack discharge.

Per-set load before and after

With synchronised sets sharing load in proportion to their ratings, each set carries the same percentage of its own rating. That percentage is total load divided by total capacity.

Before: 650 kW ÷ 800 kW = 81.25%. Each 500 kVA set carries 81.25% of 400 kW = 325 kW. Check: 325 + 325 = 650 kW.

After: total capacity is 400 + 400 + 808 = 1,608 kW. At peak, 1,300 kW ÷ 1,608 kW = 80.85% (rounded).

Set	Rating (kVA)	Rating (kW at 0.8 pf)	Load before (kW)	% before	Load after, peak (kW)	% after
Set A	500	400	325.0	81.25%	323.4	80.85%
Set B	500	400	325.0	81.25%	323.4	80.85%
Set C (new)	1,010	808	n/a	n/a	653.2	80.85%
Total		1,608	650.0		1,300.0

Check: 323.4 + 323.4 + 653.2 = 1,300.0 kW.

The striking point is that peak load per existing set barely changes: from 325 kW to 323.4 kW. Looking only at total load doubling would wrongly suggest the existing RECDs are undersized. The real changes are elsewhere.

The low-load shift

The new shift runs overnight with a much lighter load: about 400 kW. If all three sets stay on line, each runs at 400 ÷ 1,608 = 24.9% of rating. Set A and Set B would each carry about 99.5 kW, and Set C about 201.0 kW. That is a low-load condition that cools the exhaust and can slow passive regeneration of a filter-type RECD.

Better options for the night shift:

• Run Set C alone: 400 ÷ 808 = 49.5% of rating. This is a much healthier operating point for the engine and the RECD.
• Run Sets A and B only: 400 ÷ 800 = 50.0% each. This keeps the older sets exercised and gives Set C rest.

Either option needs a load-dependent start-stop scheme in the synchronising panel, with enough spinning reserve for the largest load step. The synchronised generators and load sharing guide covers how RECDs behave on a shared bus.

Contingency cases

Suppose the plant sets a planning limit of 90% of rating for continuous running during a contingency.

• Set A or Set B out of service: capacity is 400 + 808 = 1,208 kW. At 90%, the remaining sets can carry about 1,087 kW. The plant must shed about 213 kW of non-essential load (1,300 − 1,087).
• Set C out of service: capacity is 800 kW. At 90%, Sets A and B can carry 720 kW, so the plant must shed about 580 kW (1,300 − 720).

These cases matter for the RECDs because they define the longest periods at high load, which in turn affect exhaust temperature and back-pressure. They also remind the team that the new set is now the most important single asset on site.

Duty and run hours

Illustratively, Sets A and B rise from about 250 to 900 hours a year each (3.6 ×), and Set C is forecast at 1,100 hours. The forecast assumes a pending grid connection upgrade arrives about 14 months after expansion and that the overnight shift relies heavily on DG power until then. More hours means more particulate collected per year, so the cleaning and inspection interval for the RECDs on Sets A and B needs review even though their peak load is unchanged. Understanding the pattern of hours, not just the total, is covered in generator load factor and duty cycle.

Back-pressure budget for the rerouted exhaust

The exhaust for Sets A and B is being extended by about 12 metres with two extra bends to clear the new hall’s roof. The illustrative figures for Set A are:

Item	Value (kPa)
OEM maximum allowable back-pressure (illustrative)	7.5
Measured at full load today, RECD recently cleaned	5.2
Estimated addition from new route (12 m, 2 bends)	1.4
Allowance for RECD loading between cleanings	0.8
Projected worst case	7.4
Remaining margin	0.1

Check: 5.2 + 1.4 + 0.8 = 7.4 kPa, leaving 7.5 − 7.4 = 0.1 kPa.

A margin of 0.1 kPa is too thin to rely on, especially with the run hours rising. The exhaust designer increases the pipe diameter for the new section by one size, which brings the estimated addition down to about 0.6 kPa. The projected worst case becomes 5.2 + 0.6 + 0.8 = 6.6 kPa, with a margin of 0.9 kPa. The same calculation is repeated for Set B, and done from scratch for Set C using its own OEM limit and RECD data.

Which RECDs need re-review

Set	Why review is needed	Review type
Set A	Exhaust rerouted (back-pressure change), run hours up about 3.6 ×, new night-shift low-load risk, new BMS link	Back-pressure recalculation, duty and maintenance review, post-modification test
Set B	Same as Set A	Same as Set A
Set C	New engine, new DG room, new stack	New RECD selection, type-approval documents, commissioning and acceptance tests, consent inclusion

Notice that neither Set A nor Set B needs a new RECD in this scenario. They need verification that the existing devices still work within the new route and duty. If the per-set load had risen sharply, or if either engine had been replaced, the answer would be different.

Illustrative timeline

Month	Expansion construction	RECD and compliance activity
0	Design freeze for new hall	Collect DG load logs, run hours and OEM data for Sets A and B; record baseline readings
1	Tender for civil and electrical works	Issue RFQ for Set C’s RECD; brief consultant on consent amendment
2	Foundations for new hall and DG room	Back-pressure budgets for all three sets; agree route and pipe sizes
3	Structure and roofing	Submit consent amendment; place RECD order for Set C; agree monitoring specification with BMS integrator
4	Roof penetrations and DG room services	Install new stack supports; plan backup cover for Sets A and B modification
5	Set C delivered and placed	Set C’s RECD delivered and inspected; reroute Set A exhaust during a planned weekend outage
6	Electrical tie-in and synchronising panel	Reroute Set B exhaust; post-modification readings on Set A and Set B
7	Load bank and commissioning	Set C commissioning with RECD fitted; acceptance tests; BMS point checks
8	Production trial in new hall	Night-shift start-stop logic tuned; first month of trend data reviewed
9	Handover	Records updated; consent documents filed; revised maintenance schedule issued

The key rule in this sequence: Set C does not carry production load until its RECD is installed, tested and included in the consent paperwork.

FAQ

Does doubling a factory’s load mean every existing RECD must be replaced?

Not necessarily. An RECD is sized to the engine it serves. If the engine is unchanged and the per-set load stays within its normal range, the device may remain suitable. What usually needs review is the duty (run hours), the exhaust route, the low-load periods and the maintenance interval. Replacing an engine with a larger one is different: that needs a new RECD selected for the new engine.

Can the new generator use an RECD removed from an older set?

Only if the supplier confirms it suits the new engine’s displacement, exhaust flow, back-pressure limit, connections and mounting, and the certification and consent records allow it. In practice, a 1,010 kVA engine and a 500 kVA engine have very different exhaust flows, so a transfer between them is unlikely to be suitable. Read can an RECD be transferred to another diesel generator? before considering it.

Do we need to tell the SPCB about a new DG set before it runs?

In most cases, yes. Adding capacity or changing the DG configuration usually requires a consent amendment or a fresh application, and the rules differ between states. Check with your SPCB or consultant at the design stage, and plan for the new set to be compliant, with its RECD fitted, from its first production run.

Should the existing RECDs be retested after the expansion?

If their exhaust routes, engines or duty have changed significantly, a retest or at least a documented set of comparison readings is sensible. Record the same parameters before and after the change, at the same load and warm-up conditions, so the comparison is meaningful.

Talk to Aceget about your expansion

Aceget supplies CPCB type-approved Retrofit Emission Control Devices for DG sets from 25 kVA to 2500 kVA. If your factory is growing and you need to work out which sets need a new RECD, which need a review and how the work fits your construction programme, share your DG details, load data and layout drawings with us. You can review our certifications or contact our team to discuss your project.

Related Reading

• How to Specify an RECD for a Future Generator Load Increase
• RECD Planning for Generator Banks That Rarely Run All Units
• Can a Shared Spare RECD Support a Fleet of Generators?
• How to Build an RECD Asset Register for a Multi-Site DG Fleet
• Can RECD-Equipped Generators Operate in Solar-Battery Hybrid Systems?