Cooling load
The cooling load is a heat load to be dissipated convectively from a room , which is necessary in order to achieve or maintain a given room air condition. According to VDI 2078, it is divided into external cooling loads and internal cooling loads.
The cooling load is calculated in Germany according to VDI 2078: 2015, in Austria according to ÖNORM H 6040.
External cooling loads
External cooling loads are those cooling loads that bring energy into the building through solar radiation and warm outside air and thus lead to its warming. This includes:
- Heat flow through external walls
- Heat flow through roofs
- Transmission heat flow through window
- Radiant heat through window
- Heat input through joint ventilation
The sum of these factors results in the external cooling load of a building or room.
Internal cooling loads
Internal cooling loads are understood to be those cooling loads that result from energy conversion processes that take place inside the room or building in question and lead to the room being heated. This includes:
- Heat output of around 120 watts per person
- Heat dissipation through lighting
- Machine and device heat
- Heat input through material throughput
- Heat through chemical reactions
- Heat flow from neighboring rooms
Latent heat loads
A special form of internal cooling loads are latent heat loads. These are not noticeable because the room has not (yet) warmed up through them. This is the enthalpy of the water vapor contained in the room air. When this water vapor condenses (e.g. when the room is cooled down by an air conditioning system ), the enthalpically stored heat energy of the water vapor is released and supplies the room with energy, which now leads to heating and thus additional power requirements for the air conditioning system.
The sum of these factors gives the internal cooling load of a building or room.
Procedure
VDI 2078 distinguishes between a simplified and a detailed procedure. The special feature of the procedure is that the room cooling load is not calculated for any point in time, but for a specific maximum point.
For this purpose, the cooling load of each individual room for particularly hot months of the year is calculated several times at intervals of one hour using an example day (e.g. July: 9:00 a.m., 10:00 a.m., 11:00 a.m. ... 5:00 p.m. , 6 p.m.). It is particularly important to ensure that the storage mass of the walls in relation to the area of the room can cause enormous time delays, which lead to very different temperature behavior of different rooms in the same building. In general, it can be said that small rooms, due to the larger mass / surface ratio, have a greater time delay in heating (and cooling) than larger rooms (built with the same construction method).
To determine the building cooling load, the sum is formed from the hourly results of the room-by-room consideration (i.e. all 11:00 a.m. calculations of the respective day are added, all 12:00 p.m. calculations etc.). The building cooling load represents only the maximum of all these sums.
Due to this multiple calculation, the procedure is more complex than determining the heating load , which only needs to be considered for a single point in time, since time delays are not relevant here.
Norms
A calculation that is valid for Germany is contained in VDI 2078: 2015.
A calculation that is valid for Austria is contained in ÖNORM H 6040.
The cooling heat requirement can be calculated using ÖNORM B 8110-8.
Individual evidence
- ↑ At an ambient temperature of 20-23 ° C, a person emits around 120 watts of heat, according to VDI guideline 2078. Quoted in: Klaus Usemann, Horst Gralle: Bauphysik: Problems, tasks and solutions , p. 18, Springer Verlag; accessed in January 2017