Calculate a space's cooling and heating loads

Each space on an HVAC project has its own sheet on Space Loads. Kelvin works out its peak cooling load hour by hour by the ASHRAE Radiant Time Series method, its steady heating load, and what the supply air has to do to hold it.

1. 1

   Select the space in the Space ledger, or choose Add space for one you won't draw on the building plan.

2. 2

   Under Indoor design condition, enter the Cooling dry bulb, Relative humidity and Heating dry bulb, then the Height under Geometry.

3. 3

   Enter the space's People, Lighting and Equipment, each with its schedule, and its Infiltration.

4. 4

   Under Construction and sun, choose the Non-solar RTS and whichever other rows the sheet asks for.

5. 5

   Read the results beside the sheet, then choose Save space.

The results follow what is on the sheet, saved or not. They appear once the sheet is complete and the project's design conditions allow them.

• –The two radiant time series are the space's construction class: how much of a radiant gain appears as cooling load in later hours. The Solar RTS is needed only while a window has no interior shade.
• –The Default sol-air row applies to any outdoor surface that doesn't name its own. Ground reflectance is needed as soon as the space has an outdoor surface that doesn't face straight up, such as one outdoor wall.
• –Left unset, the Daily-range profile falls back to a default row in Kelvin's library.
• –Process moisture is water released into the space by a process, not by people. It is a latent gain only.

A space drawn on the building plan takes its floor area, walls, roof, floor and windows from the drawing, shown under Envelope — from the building plan, and you edit them on the plan. A space that isn't drawn is entered under Surfaces and Windows: Add wall, Add roof, Add partition or Add floor, then Add window for each window in an outdoor surface. Areas are gross; each window is taken off its surface.

• –People: the Occupants and an Activity row, which carries the sensible and latent gain per person. Leave the count blank for an unoccupied space.
• –Lighting: Entered as W/m² of floor or total watts, with a Luminaire type. Only the luminaire row's space fraction reaches the space; the rest goes to the return air.
• –Equipment: each item takes a Library row, which carries its gains, or a Radiant split with its sensible gain (and any latent gain) entered per item.
• –Each gain has a 24-hour schedule, hour ending 1 to 24 in local standard time. Drag the graph to set each hour, or use Occupied with a level and Fill, then shape it. You can copy another schedule on the sheet, or Clear it.
• –A blank hour is zero. A schedule left completely blank counts as not entered, and that gain won't calculate until it is set. Kelvin offers no typical profiles.

Choose a Method: Air changes per hour, Litres per second or From a library rate. Work it out from a leakage area… applies the ASHRAE Fundamentals Ch.16 Basic Model to an effective leakage area, the storeys, a local shelter class, a temperature difference and a wind speed, with where the leakage area and wind speed came from. A drawn space can add its leakage area up from its outdoor walls, roof, floor, windows and doors, each on a leakage row you choose; a part left unchosen adds nothing. Use as the infiltration rate writes the flow in, in litres per second. The chapter gives that model for houses of one to three storeys, so it isn't for a commercial building. Tick Scheduled to vary the rate by the hour; unscheduled, it runs at full rate all day.

• –Peak cooling load: the design month and hour (local standard time, no daylight saving), the sensible, latent and total load, and the load per floor area.
• –At the peak hour: each gain's share of that hour's load. The total isn't the sum of the gains entering the space, because radiant gains appear as load in later hours.
• –Design-day profile: the peak month's load hour by hour.
• –Heating load: steady-state loss through each surface and window at the heating design dry bulb, plus infiltration. No credit is taken for sun or internal gains.
• –Supply air and dehumidification: type a Trial supply dry bulb to see the room sensible heat ratio, the supply airflow it would need and the dew point the coil would have to reach. It is a check; the air system sets the real supply temperature.
• –Basis: the method, and every reference row the loads used with its source and edition.

• –Save space lists what is missing. Every figure on the sheet is yours or a reference row's: Kelvin fills in none of them.
• –A notice above the results names what the project's design conditions still lack: the latitude, longitude and UTC offset, at least one complete design month, the heating design dry bulb or the elevation. Complete them on Design Conditions.
• –Ground-contact surfaces are left out of the cooling load. The heating load takes them only when the project has a ground temperature, and otherwise leaves them out and says so.
• –A space saved before the project's last save reads as stale in the ledger. Open it and save it again.

If a table the sheet needs isn't in Kelvin's library yet, see Missing reference tables.