What’s the best way to calculate heating and cooling demand in the case you don’t have an all air system? When I use Ideal Air, the amount of ventilation determines the maximum cooling and heating that can be supplied to the room. In reality, that limit isn’t there. But if I use DOAS, then I get the energy consumption, not the energy demand. Also, for some reason, when I use DOAS, I cannot switch off the cooling. Even when I use a schedule with setpoint at 50°C, it’ll use 28°C as setpoint in the calculations.
Can anyone help me with this? I keep struggling.
When I use ideal air:
- I often get no cooling demand, even though the building is overheating and should be cooling. I have a clear cooling schedule, yet, it’s not cooling.
- the cooling and heating power is limited by the ventilation volume. In reality, we limit the amount of fresh air according to occupancy, but we mix with internal air to get enough volume to cool or heat the room.
When I use DOAS:
- then I do get cooling, but can’t switch it off. I’ll always cool, even when I use a schedule with a setpoint at 50°C.
- I can’t get the heating and cooling demand, I get the electricity consumption instead.
I would prefer to use Ideal Air all the time, since I really want the heating and cooling demand. But my results are useless if it’s not cooling and if I can’t indicate that the max cooling and heating power is actually higher than what the program thinks.
I’ve sent you a PM. Thank you.
Hi @TineVB
I reviewed your simulation and noticed several issues.
First, your schedules are overlapping. The stream filter you applied is not functioning as intended: you’re feeding values such as 18 (which are well below 50) and then excluding 50, but there is no value of 50 anywhere in your temperature setpoints. If you manually set the Gene Pool to 50 and remove the stream filter, you’ll see that the cooling system switches off.
Regarding the HVAC setup:
-A DOAS is not an HVAC system by itself. It is simply a fresh-air delivery system for the building’s HVAC. Given the EPW you selected, which represents a cooling-dominant European climate, it’s expected that the outdoor air is cool unless the DOAS is explicitly equipped with properly sized coils (e.g., cascade heating/cooling).
-The Ideal Air is a diagnostic tool for architecture-driven load estimation. It does not simulate real HVAC physics. If you rely on it for system-level techno-economic analysis, the results will be fundamentally invalid.
Could you check these points on your side and let me know?
Thank you for your reply.
I’m not sure what you mean about schedules overlapping. The 18 values are in the heating schedule, nowhere in the cooling schedule. Even when I enter the cooling schedule directly and don’t use the stream filter, the result is the same. I only use that stream filter because I want to do the calculation with and without cooling. But even with cooling, it’s not cooling. The room is overheating, temperatures go way above 30°C, and still cooling is 0. I don’t know why it’s doing that. Even when I set my cooling schedule to extremely low temperatures, it refuses to cool.
I entered a simple HVAC system to check if it does cool when I use that, and then it does cool. But then I don’t get the load balance anymore, don’t get heating and cooling demand profiles. I really need to those profiles. End use is not very useful, it’s too much of a black box. I really need to see what’s happening, need those intermediate steps.
The most common HVAC system is a central air handling unit for fresh air, demand controlled, and heating and cooling via climate ceilings. I could model that HVAC system to get comfort metrics. But I still need the heating and cooling demand profiles. And those I only get when use Ideal Air. But with Ideal Air, the cooling and heating is limited if I use demand controlled ventilation, it’s limited anyway if I use the correct air volume. The only way is to increase the ventilation volume, and then increase the efficiency of the heat recovery (or set it to 1, in that case, I need to calculate ventilation losses seperately).
I now noticed that if I don’t enter a value for ‘summer design day’ and ‘winter design day’, it does cool.
So that issue is now resolved.
And that cooling is limited by the ventilation volume is also resolved, now that those values are gone. It’s really strange, that entering a simple value for cooling set point and winter set point, caused so many issues and completely altered my calculations.