Fixed temperature air

Richard - you should consider fixed temperature air as a tempered air supply to the zones or air flow from another space. The manual advises:

This could be a fixed air flow from another space, or a tempered air supply to rooms. The fixed temperature air flow rate can be specified as an air change rate, an air flow per person or an air flow per square metre. The temperature and % saturation of the fixed air supply must also be specified. Each room included in the calculation will be subject to the specified fixed temperature air supply, which will be assumed to occur throughout the day and night.

Duncan,

Thank you for the prompt response.

For some reason I am having difficulty accessing the manual through the software, I have informed our IT about the issue but have not heard back from them. Its not something which you are able to send me in PDF format is it?

With regards to my original question, I was trying to model a room (both heat gains and heat losses) where fresh air is introduced to the room un-conditioned on a l/s/per basis.

For the heat gains calculation I used the 'fresh air loads' section in the design data tab, and selected 'fresh air introduced locally to the rooms' and input 10l/s/per.

For the heat loss case there isn't a 'fresh air load' section under the design tab, so I used the 'fixed temperate air' and specified 10l/s/per at 31deg and 37% sat (Summer external design conditions of 31deg DB & 20.5 WB).

Is the approach that I have taken correct?

Also under the heat gain calculation, what's the difference between the 'fixed temperature air' and 'fresh air loads', as they appear to do the same thing?

Regards

Richard

Apologies for the heat loss case as there isn't a 'fresh air load' section under the design tab, I used the 'fixed temperate air' and specified 10l/s/per at -4deg and 99% sat (winter external design conditions of -4deg DB & 100%sat).

Richard

A further breakdown of the Fresh Air options:

A fresh air load can optionally be included in the load calculation.  Fresh air will be supplied to all included rooms using one of the following criteria:

 

• Air change rate
• Fresh air requirement per person
• Fresh air requirement per square metre

Fresh air may be introduced locally to rooms, in which case it will affect the room load.  Fresh air from the central plant will form part of the supply air and will be a load on the central plant.  Conditioned primary air will be supplied at the defined supply temperature, with optional supply humidity control.  Conditioned primary air will affect both room loads and central plant loads.  If conditioned primary fresh air is specified and this fresh air requires heating at the central plant, when the building requires cooling (or vice versa), then the fresh air heat load will be excluded from the central plant loads.  This will be indicated on the hourly results of total load by an asterisk against hourly values.

Where you aren't considering a defined supply temperature, then the basis for this air is the outside hourly temperature, rather than a fixed temperature for the whole period.

With regards your issues with the manual - that would suggest to me that you are using version 25 with a server/client installation? If so then this document should help you out.

Duncan,

So with regards to the heat gain scenario, if I have fresh air introduced into the room unconditioned then the option to use is 'fresh air introduced locally to rooms' and then just specified a fresh air type i.e. air change or per person?

With regards to the heat loss scenario, if I have fresh air introduced into the room unconditioned, then how do I go about modeling this?

Regards

Richard