Zone energy
The report shows the sensible heat balance for a single or a group of zones. (See the Heat balance diagram for a total (wet and dry) heat balance).
Data is presented for each month as well as for the whole simulation period. In addition, each heat flux is divided into the "during cooling," "during heating" and "rest of time" categories. A gain as for example heat from a piece of office equipment, is beneficial when it occurs when the zone has a heating need. Similarly it is harmful when there is a cooling need. The algorithm for this categorization is further described below.
An overview and a specification of envelope transmission losses are presented. The control volume is inside walls, at the ceiling and at the floor surface. However, in the case of embedded (slab) heating/cooling, the control volume includes the activated layer and thereby contains significant thermal mass. The overview has the following columns:
Category | Comment |
Envelope and thermal bridges | Heat gained through external walls, floors, roofs and through thermal bridges. |
Internal walls and masses | Heat gained through internal walls, floors, ceilings and internal masses. |
Window and solar | Net heat gain through external windows from solar radiation and heat transmission through pane and frame. Advected heat through open windows is included in Infiltration and openings. Note that transmission only is presented in a separate table. |
Mechanical supply air | Heat supplied by mechanical ventilation. |
Infiltration and openings | Heat supplied via air from leaks and openings. For systems with only mechanical exhaust ventilation, all supply air will be accounted for here. |
Occupants | Heat from people in the zone, excluding heat from perspiration. |
Equipment | Heat from equipment in the zone, e.g. computers etc. |
Light | Heat from artificial lighting. |
Local heating units | Heat from controlled heating units, e.g. radiators, fan coils etc. |
Local cooling units | Heat from controlled cooling units, e.g. chilled beams, fan coils etc. |
Net losses | Heat from pipes, ducts etc., the leakage from which has been defined in Extra energy and losses. |
The time evolution of the individual terms can be followed by selecting Log sources in the List of output objects. This diagram can be used to display a sensible only heat balance for the zone. Note: This balance will not generally sum to zero, since latent sources are neglected and thermal mass can be included in the control volume. The control volume for the Zone energy object includes any embedded heating or cooling coil in the structure and may therefore have a significant thermal mass.
The table for Envelope transmission shows heat flux via transmission only through the building envelope. It has the following columns:
Category | Comment |
Walls | Heat gained through external walls |
Roof | Heat gained through the roof. |
Floor | Heat gained through any external floor (towards ambient or the ground). |
Windows | Heat gained via transmission only, through windows and frames |
Thermal bridges | Heat gained through thermal bridges. |
The algorithm for categorization will keep track of each gain term and integrate it separately for the categories "during cooling" and "during heating." When the zone temperature is above or slightly below the Max temperature as specified in the Setpoint collection, all gains are collected in "during cooling". This is also done when no mechanical cooling exists, i.e. in this case the Max temperature is regarded as "Maximum preferred temperature."
Similarly, a gain is collected in "during heating" when the temperature is below or slightly above the Min setpoint. "Slightly" in both cases is defined as half of the throttling band for proportional controllers, i.e. by default 1°C. When the distance between Min and Max setpoints is getting too small, "slightly" is instead interpreted as 25% of the dead band.
A heat gain that occurs while the zone temperature is within the dead band (minus "Slightly" on each side), is also integrated. However, this integration is done with an exponentially decaying weighting factor that accounts for if the heat gain is old or new. For example, a heat gain contribution that occurred several days ago – assuming the zone is floating in the dead band – is forgotten, while a gain that is occurring just as the zone about to leave the dead band is counted almost fully. The time constant for this memory is by default 24h but can be selected in System parameters.