The Unit They Chose Was Half the Capacity They Asked For

What the integrator asked for

An HVAC integrator was retrofitting cooling onto existing air source heat pumps. The project turned on a capacity mismatch nobody had noticed.

Initially their brief asked for a component assembly, possibly just a coil and a condensate tray, to fit a 150mm round duct system.

What the original brief specified

• Cooling capacity of 3 to 4 kW, on 7C inlet and 12C outlet chilled water.
• Next, a drain connection for condensate.
• Meanwhile five sample units for performance validation.

Then the scope changed. After reviewing our catalog they selected a standard fan coil unit as the base platform, which turned a component design into a product modification.

Now they wanted three things: an EC motor in place of the AC one, a custom return air box, and CE certification for the modified assembly.

Finding the capacity mismatch

The motor upgrade was straightforward. However, the first thing our review found was not.

The numbers did not agree

Here the unit they selected provides 1.9 kW of cooling. Their original brief asked for 3 to 4 kW.

A larger model in the same family delivers 3.6 kW and would have met the target. However, it is physically bigger, and their chosen unit measures 750 by 490 by 235 mm.

So there are two readings. Either the capacity target still stands and the selection is wrong, or the compact envelope now matters more and the capacity target has moved.

Why we raised it instead of assuming

Certainly the easy path is to assume they changed their mind, build what was ordered, and let the capacity mismatch surface at commissioning.

That is a poor outcome for everyone. A retrofit that under-delivers on cooling gets blamed on the equipment, and by then the units are installed.

So the discrepancy was put back to the customer as a question rather than resolved internally. Whichever number is the real requirement, it is theirs to confirm.

The motor upgrade itself

The standard unit uses a three-speed single-phase AC motor, which cannot give the control their system needs.

So we picked an EC motor that fits the existing fan mounting and housing. Consequently the chassis tooling stays untouched, which is most of what would make this expensive.

Meanwhile the SmartEC control accepts 0-10V or PWM directly from a building management system. Furthermore it lowers both energy use and noise against the AC original.

What it cost

A conversation, and probably a delay. Raising a discrepancy slows a project down at the point where everyone wants to move.

Even so, it is cheaper than discovering a capacity mismatch after five samples become a production order.

Technical Specifications

The cooling capacity row below is where the capacity mismatch sits against the original brief.

Air Flow (High/Med/Low)	360 / 260 / 170 m³/h
Cooling Capacity	1800 W
Heating Capacity	2700 W
Input Power (AC Motor)	44 W
Noise Level	40 dBA
Dimensions (L x W x H)	750 x 490 x 235 mm
Water Flow	310 kg/h
Water Pressure Loss	≤30 kPa
Inlet / Outlet Water Pipes	3/4 inch internal thread
Maximum Allowable Working Pressure	1.6 MPa
Base Motor Type	AC 220V 50/60Hz, Single-Phase Capacitor
Upgraded Motor Type	Longwell EC Motor with SmartEC™ Control (0-10V/PWM)

Technical Documentation

Here the product data sheet provides HVAC engineers with the performance parameters for the entire FP fan coil series, showing airflow, cooling capacity, and power draw for each model.

LWFC-34WA-07 Technical Drawing

Here the engineering drawing provides OEM procurement managers and system integrators with the exact dimensions, connection points, and component layout for the LWFC-34WA unit.

If your brief and your selection disagree

A capacity mismatch between the brief and the selection is common and easy to miss.

• Restate the duty when you change the selection. Picking a unit from a catalog after writing a performance brief is where the two drift apart. A one-line confirmation of the capacity target with the new model number prevents most of it.
• Ask the supplier to check the brief against the part. A supplier who simply quotes what you name is not doing you a favor. Ask explicitly whether the selection meets the stated duty, and treat silence as an unanswered question.
• Say which constraint wins if they conflict. Capacity and envelope pull against each other. Naming which one is fixed lets a supplier propose the right compromise rather than guessing at one.
• Confirm the water conditions with the capacity. A cooling figure means nothing without the flow and temperature it was measured at. Chilled water at 7C in and 12C out is a different rating point from 6C and 12C.

See our fan coil unit range, the EC forward curved fan section, or HVAC systems. Efficiency rules come from ASHRAE 90.1.

Questions about this retrofit

What happens if the capacity target was the real requirement?

Then the selection changes to the larger unit, and the physical envelope grows with it. That is a design decision on the customer side rather than a supply one. What matters is that it gets made deliberately, before samples become production.

Why does the envelope matter so much on a retrofit?

Because the space already exists and was not designed for this kit. Ceiling voids, service corridors and duct routes are all fixed. A unit that meets the duty and does not fit is no solution. So in a retrofit brief, compact dimensions often outrank capacity.

Can an EC motor make up part of the capacity gap?

No, and it is worth being clear about that. An EC motor improves efficiency, control and noise. Cooling capacity comes from the coil, the water conditions and the airflow across it. Changing the motor does not change the kilowatts available.

Does modifying a standard unit affect its CE marking?

It affects who is responsible for it. A modified assembly needs its own conformity assessment rather than inheriting the original. That was part of this scope, and it is worth agreeing early who performs and holds it.

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