Hello
I have issues simulating a water cooled coil (software limitations), and so I’m trying to simulate an equivalent thermodynamically system. I want to know if this methodology is valid for LEED documentation.
I’m simulating an air cooled coil with an equivalent COP. The equivalent COP is the ratio between the water cooled coil cooling capacity and the electric power, which includes compressor and pumps & cooling tower power in the condenser loop.
Please let me know what do you think about the equivalency.
Regards,
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5867 thumbs up
January 22, 2020 - 10:51 am
So first of all you should be using software that has the capability to model the systems in your project. Modeling a water cooled coil is something common to most modeling software so it is not like this is some sort of exotic system type. Without seeing the math behind your description it will be difficult to say if you have equivalency. So make sure to provide that to the reviewer. Also you should make sure that the equivalency you seek is conservative (i.e. likely to produce results that will show less savings than would actually be generated).
Nicolas Martinez Ochoa
Energy ConsultantSIMGEA
5 thumbs up
January 22, 2020 - 12:04 pm
Thank you for your answer Marcus.
I agree the water cooled coil is not an exotic system, but the way this HVAC system is connected is atypical.
To calculate the equivalent COP: firstly, I calculated the electric power in the water cooled coil with its COP and its cooling capacity. Secondly, I added to the electric power the pump power and the cooling tower fan power. Finally, I divided the water cooled cooling capacity by the total electric power calculated in the last step. As a result, I simulated an equivalent air cooled 3.0 COP instead of a water cooled 3.53 COP.
Do you think is it reasonable?
Jean Marais
b.i.g. Bechtold DesignBuilder Expert832 thumbs up
January 23, 2020 - 4:04 am
The rated COP is valid only for one operation point. This one operation point includes several variables. For example, it is the cooling generated when
-Toutdoor is 27ºC
-RHoutdoor is 60%
-Return Cooling Fluid from the Condenser is 37ºC
-Supply Cooling Fluid to the Condenser is 48ºC
-Cooling to the building Fluid is 6ºC
-Cooling fluid return from the building is 14ºC
-etc.(depending on technology used)
That is ONE operating point used to define the COP of a system. The rated COP of the system is for conditions as per the rating test for that equipment. You can't use a rated COP for a simulation as constant. That's why we need to enter performance curves or matrix that cover all the possible conditions that could occur in the year. Getting an annual equivalent COP for that is pretty difficalt to support with a narritive. It would at the very least only be valid for a test reference weather set and would be specific to it.
There are some data derived standards that calculate in this way like the DIN V 18599, but suffice to say that they make a lot of assumptions and ironically require almost as detailed an input as for a fully fledged simulation for far less accuracy.
Nicolas Martinez Ochoa
Energy ConsultantSIMGEA
5 thumbs up
January 24, 2020 - 11:10 am
Thank you Jean. I will try to simulate the HVAC system as accurate as posible.