Design and duty calculation
Room-by-room heat gains, fresh-air rates to Building Regulations Part F, and a coil selection with the psychrometrics done rather than assumed. You get the state points, not just a kilowatt figure.
Heating, ventilation and air conditioning · Sheffield
We design the coil before we sell you the plant.
Air conditioning, ventilation and heat-pump installs for commercial buildings across South Yorkshire. A survey is £340 and it comes back with the state points, the air volumes and the drain load — not a kilowatt figure and a hopeful smile.
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The idea the company is built on
A coil can only take water out of the air if it is colder than the air's dew point.
Above that line a coil takes heat out and nothing else, and the air leaves carrying exactly the moisture it arrived with. Below it, water leaves the air and has to go somewhere. Half the plant we are called out to was sized on the first case and installed into the second.
Scroll the coil below and you are moving through the fin bank, front to back. The state point on the chart is computed, not drawn, and so is the water coming off the fins.
Coil 01 — condensing
MUA-1, Cawdrey Gate
Make-up air, 100% outside air, six-row chilled-water coil at 6/12 °C.
| dry bulb | humidity ratio | RH | enthalpy | |
|---|---|---|---|---|
| Air on | 28 °C | 10.6 g/kg | 45% | 55.2 kJ/kg |
| Air off | 12.7 °C | 8.39 g/kg | 92% | 34 kJ/kg |
| Duty | 51 kW total | 37.7 kW sensible | 13.37 kW latent | SHR 0.74 |
| Condensate | 19.1 litres per hour to drain | |||
Air on at 28 °C and 45% RH has a dew point of 15.0 °C. The coil surface is at 11 °C, four degrees under it, so the state runs down a straight line aimed at that surface condition — a point sitting on the saturation curve. It falls to the left and downward, and the downward part is water leaving the air: 19.1 litres an hour, which is the drain everybody undersizes. The air stops at 92% rather than on the curve because a tenth of it slips between the fins without touching them.
The same coil, the same code, a different room
And this one never makes a drop.
A sealed switchroom has a large load and almost no moisture in it. Its air recirculates at 24 °C and 30% RH, which puts the dew point at 5.4 °C — five and a half degrees below the coil surface. There is nowhere for water to go, so the process line runs dead horizontal, the sensible heat ratio is 1.00 exactly, and the drain pan stays dry every hour of the year.
Coil 02 — sensible only
CCU-1, Thrapp Hill
Close control, full recirculation, sealed room with no fresh-air provision.
| dry bulb | humidity ratio | RH | enthalpy | |
|---|---|---|---|---|
| Air on | 24 °C | 5.53 g/kg | 30% | 38.2 kJ/kg |
| Air off | 12.3 °C | 5.53 g/kg | 63% | 26.3 kJ/kg |
| Duty | 20 kW total | 20 kW sensible | 0 kW latent | SHR 1.00 |
| Condensate | none — the coil surface is warmer than the entering dew point, so no water can leave the air | |||
Nothing was switched off to make that happen. It is the same component and the same arithmetic; only the air entering it is different.
What we do
Install
Air-handling plant, chilled water, VRF and air-source heat pumps, ductwork to DW/144, and the electrical and controls work that goes with them. Our own fitters, no labour-only subcontract.
Commissioning
Air volumes proportioned and recorded to CIBSE Commissioning Code A, water systems balanced, and every coil checked against its design condition on the day. Signed sheets, not a tick box.
Service and breakdown
Planned maintenance on a fixed visit rate, statutory F-Gas leak checks logged, and a four-hour response for contract sites. Most breakdowns we attend are condensate, filters or controls.
Published rates
| Site survey and duty calculation Measured heat gains, air volumes and a psychrometric check on every coil. | £340 | fixed, credited against the install |
|---|---|---|
| Planned maintenance visit Filters, belts, condensate, refrigerant leak check, F-Gas log. | £185 | per visit, per plant item |
| Breakdown call-out Contract sites carry a four-hour response, seven days. | £96 | first hour, £64/h after |
Coil notes
What we write down after a call-out.
Tell us what the building does and we will tell you what it needs.
A survey covers the heat gains, the air volumes, the coil condition and the drain. If the answer is that you do not need us, that is what the report will say.