An air system is one AHU, fan coil, packaged unit or dedicated outdoor-air system. Kelvin sums the loads of the spaces it serves hour by hour, then carries that block load through mixing, the coil and the fan to the supply state, at the project's cooling design condition.
- 1
Choose Add air system, then tick the spaces it serves under Spaces served. Each needs a saved result on Space Loads.
- 2
Set its Outdoor air, how its Supply air is Sized by, and where its Fan heat comes from, with the source of any rate you enter.
- 3
Choose Save air system, then read its block load, coil and psychrometric chart beside the sheet.
The sheet
- System kind and Coil media describe the system. They don't change the calculation, which is the same air-side process for each.
- Outdoor air is a rate in L/s at the outdoor design state, a Fraction of the supply by dry-air mass, or a Library rate applied to each served space's people and floor area. An entered rate needs its source.
- Supply air is sized by Supply temperature (the airflow follows) or Supply airflow (the temperature follows). One is given, never both.
- Under Coil leaving condition, tick The coil leaves the air colder than the supply when the coil must dehumidify below the supply temperature. Kelvin then works out and reports the reheat.
- Fan heat is Not included, read from a saved Fan record on Fans, or Entered with its source. Fan position has no default: Draw-through adds the heat after the coil, Blow-through puts it on the coil.
- A Diversity factor applies to the coincident peak only, and only with its source.
- Under Heating, the heating coil is sensible only: the heating design outdoor air mixed with the first served space's heating temperature, heated to the Heating supply dry bulb.
What the results show
- Block load: the coincident peak (the hour the served spaces are hot together) beside the sum of each space's own peak, with the difference named.
- Psychrometric chart: the process drawn at the site's own barometric pressure, through six state points: outdoor, return, mixed, coil entering, coil leaving and supply.
- State points: each point's dry bulb, wet bulb, dew point, humidity ratio and enthalpy.
- Cooling coil: total, sensible and latent duty, sensible heat ratio, apparatus dew point, bypass factor and condensate, with the reheat and heating coil where they apply.
- Airflow: supply and outdoor airflow, the outdoor-air share and the supply mass flow.
Limits
- The return air is taken at the first served space's indoor design state. If the served spaces differ, a note says so. Plenum and return-fan gains are not added.
- Each space in Spaces served shows whether it is calculated, stale or not calculated. The coil waits until every served space has a saved cooling result. A stale space is still summed with its saved figures, so save it again on Space Loads first.
- A month is left out of the block load unless every served space was calculated for it, and a note names it.
- With fan heat from a Fan record, the figure is read as the fan was saved. Save the air system again after the fan changes.
To place the unit and its registers, see Place an air system's unit and registers. Size its ducts opens the system's duct network on Ducts, or starts one; save the air system first.
Note
Saving an air system makes any duct network or fan calculated from it stale. The version it replaces stays in the record's history.