Missing or Zero Loads

When loads don’t appear, are partially missing, or read zero, the cause is almost always an unassigned input rather than a calculation problem. Work through the cases below. If a people, lighting, equipment, or misc. cooling load is zero only at some hours, check the space type’s schedule: see How schedules scale loads.

Loads aren’t showing at all

Three inputs stop a space’s loads from calculating at all. HVAKR leaves the load out of the results for that space instead of showing a partial value.

Missing input	Cooling load	Heating load
A space type on the space	Not calculated	Not calculated
A weather station and an elevation for the project	Not calculated	Not calculated
Building CTS Data for the project	Not calculated	Calculates normally

The most common cause is a space with no space type. The space type defines the design requirements (internal loads, ventilation, setpoints) and links them to the space geometry.

To fix a missing space type:

1. Select a space in the Spaces pane.
2. In the Space Data sidebar, assign a space type using the Space Type dropdown.

To fix a missing weather station, go to Basis of Design → Weather, enter the Project Address, and confirm that a station is selected under Weather Station. The elevation comes from the project location, or from the station when the location has none. See Weather.

To fix missing cooling loads when heating loads are present, go to Basis of Design → Building Data and select the Building CTS Data. Heating loads don’t use it. See Building Data.

Once these inputs are assigned, loads populate accordingly. See Space Types.

A space shows a low or unexpected BTU despite having exterior walls

Two different design-condition fields on the space type cause two different problems. Don’t treat them as the same issue.

Missing Summer (Cooling) or Winter (Heating) setpoint. Every envelope load (walls, windows, roof, skylights, slabs, doors) and every ventilation/infiltration load (sensible and latent) needs the matching setpoint to calculate. Without it, HVAKR zeros that entire load path for that condition. The two conditions then behave differently:

• Cooling: internal gains (people, lighting, equipment) don’t depend on the setpoint, so they still calculate. The cooling total isn’t always exactly 0 BTU. Only the envelope, ventilation, and infiltration components drop out.
• Heating: the heating load takes no credit for people, lighting, or equipment. Its only internal term is the space’s Misc. Heating Load. So without a Winter (Heating) setpoint, the heating total is that value, which is usually 0 BTU.

Missing Relative Humidity. This field affects the cooling load only. It removes the latent portion of the ventilation and general/window infiltration cooling loads. It also removes the door infiltration cooling load entirely (both sensible and latent) because HVAKR calculates door infiltration’s cooling sensible and latent loads together and needs relative humidity for both. Envelope loads and the other sensible ventilation/infiltration loads are unaffected. Heating loads don’t use relative humidity, so heating door infiltration still calculates.

To fix:

1. Go to Basis of Design → Space Types.
2. Select the affected space type.
3. Add the Summer (Cooling) setpoint, Winter (Heating) setpoint, and Relative Humidity values.

Loads will then calculate normally for every space using that type.

Envelope loads are missing

An envelope surface adds load only when it has an envelope type, and that type has the fields the load needs. If a field is missing, HVAKR leaves that surface out of the load and calculates the rest of the space. An edge with no wall type is not a wall: it adds no heat transfer and no warning (see Walls).

Walls and windows also need the space’s Slab-to-Slab Height for both conditions, and walls need its Ceiling Height for cooling. Set them in the Space Data sidebar.

What heating envelope loads need

Heating envelope loads are steady state: U-value × area × temperature difference, or F-Factor × exposed perimeter × temperature difference for slabs. They need these fields:

Surface	Needs
Walls	A wall type with an Overall U-Value
Windows	A window type with an Overall U-Value, on a wall that has a wall type
Doors	A door type with an Overall U-Value
Roofs	A roof type with an Overall U-Value. A space with no roof type has no roof load
Skylights	A window type with an Overall U-Value
Slabs	A slab type with an F-Factor, or an Overall U-Value when the slab uses a Winter External Temperature Override. A space with no slab type has no slab load

Heating loads don’t use Wall Mass Data, Window Mass Data, Roof Mass Data, Surface Absorptance, SHGC, or Building CTS Data. A missing Mass Data value doesn’t change the heating load.

What cooling envelope loads need

Cooling envelope loads need the same envelope types and U-values as heating, plus these fields:

Surface	Also needs for cooling
Walls	Wall Mass Data and Surface Absorptance on the wall type
Windows	Window Mass Data on the window type
Doors	Surface Absorptance on the door type
Roofs	Roof Mass Data and Surface Absorptance on the roof type
Skylights	Window Mass Data and SHGC on the window type, and a roof type on the space
Slabs	The same as heating, but with the Summer External Temperature Override

Without Mass Data, the walls, windows, skylights, and roofs that use that type are left out of the cooling results, for example the Cooling Sums at Peak. Their heating loads still calculate.

To fix:

1. Go to Basis of Design → Building Data.
2. In the Wall Types, Window Types, Roof Types, and Door Types tables, fill in the Overall U-Value and Surface Absorptance of each type in use.
3. Select the closest available assembly for Wall Mass Data, Window Mass Data, and Roof Mass Data. Add the SHGC for window types used on skylights.
4. In the Slab Types table, fill in the F-Factor.

Tip

The assembly does not need to be exact: the closest available type is enough to produce results. Wall and Roof Mass Data set the conduction time series (thermal mass delay). Window Mass Data sets how the window’s SHGC changes with the sun’s angle. The radiant time series comes from the Building CTS Data selection, not from these types.

Once the fields are filled in, the missing envelope loads appear in the results. See Building Data.

Infiltration CFM is lower than expected

Reported infiltration can come in low if some spaces with exterior wall area are missing a space type. This applies to every infiltration method, and to spaces with their own infiltration override.

The infiltration CFM totals for zones, systems, and the project leave out every space that has no space type. That space still contributes its wall area to the project total, so the totals diverge. A missing weather station or elevation removes only door infiltration. General and window infiltration still calculate.

To fix, confirm every space with exterior wall area has a space type assigned. Once assigned, the infiltration total updates accordingly.

Note

This is the same root cause as missing loads above: an unassigned space type silently drops that space from parts of the calculation while its geometry still shows up in area totals.