We're modelling an office building (space by space method) with a relatively big server room (50kW). We couldn't find a room type that corresponds to a server room and are wondering whether it'll be taken into account when comparing baseline to proposed building. We used "System 3" for the baseline system in the server room.
Our results for space cooling a pretty bad (-60%). When anaylzing the building it is apparent that the majority of it comes from the server room(s). 45% of cooling energy use is attributed to the server and patch rooms. The building is 23 floors with big open plan office spaces. Heating and Lighting Power are good so in total we still achieve a reduction of 27%. However we are wondering whether there might be an issue as to how these rooms might be taken into consideration in the baseline.
On the other hand the reason for the bad results could be that the facade is nearly fully glazed. G-Value of the glazing is 0.25. There are no raffstores but solar controlled internal shades. This is our first energy model with such a building and would like to know whether these are typical results. The project utilises compression type chillers iwth a COP of 3,35.
Thanks!
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
March 6, 2020 - 3:03 pm
Very hard to say if you have reasonable results without seeing all the inputs and outputs from the model.
Why are you modeling a system 3 in the baseline for these spaces?
Hagen Bork
Projektleiter Nachhaltiges BauenCSD Ingenieure GmbH
2 thumbs up
March 9, 2020 - 3:27 am
Hi Marcus,
when building the model we followed the Exception b) in G3.1.1.
"If the baseline HVAC system type is 5, 6, 7, 8, 9, or 10 use separate single-zone systems conforming with the requirements of System 3 or System 4 (depending on building heating source) for any spaces that have occupancy or process loads or schedules that differ significantly from the rest of the building. Peak thermal loads that differ by 31.2 W/m2 or more from the average of other spaces served by the system or schedules that differ by more than 40 equivalent fullload hours per week from other spaces served by the system are considered to differ significantly. Examples where this exception may be applicable include, but are not limited to, computer server rooms, natatoriums, and continually occupied security areas."
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5909 thumbs up
March 9, 2020 - 10:11 am
That system choice then sounds right to me.
When it comes to evaluating the accuracy of your outputs we find it is very helpful to do comparisons to existing building energy use. You can run your results in Target Finder. You should be able to find some data on the distribution of energy use by end use for a typical office and see how your results compare. Then when you see potential anomalies you can look back at your inputs and make sure they are accurately reflecting the expected conditions.
Hagen Bork
Projektleiter Nachhaltiges BauenCSD Ingenieure GmbH
2 thumbs up
March 10, 2020 - 8:10 am
The target finder results are kind of odd. Our proposed building saves 74,6% of energy & green house gases compared to the median properties.
The simulation results in our Software (IDA ICE) show savings of ~27% (proposed vs baseline). The difference between target finder and the ashrae simulation is so big it leaves me with more questions than before.
Christopher Schaffner
CEO & FounderThe Green Engineer
LEEDuser Expert
963 thumbs up
March 10, 2020 - 9:59 am
Apples and oranges.
Target Finder is showing saving vs the average of existing buildings from a survey conducted in 2012.
Your simulation is showing savings vs code.
Two very different baselines. You shouldn't expect the percentage savings to match.
Benjamin Weise
CSD Engineers16 thumbs up
March 10, 2020 - 10:59 am
Is there anything important to consider, when modeling server rooms (apart from setting it to System 3)?
Are 27% savings a common result for a 24 storey, fully glazed building equipped with compression type chillers, LED lighting and heat from a district heating power plant? There is no renewable energy production. U-Values are as follows: windows=1,25 walls=0,2 roof=0,22. I understand it's next to impossible to give a qualified answer without knowing the building/model properly. Maybe I rephrase the question: What are typical results for a "modern" building (which however does not excel in terms of building appliances and energy concept).
our results (savings) are:
heating: 53%
ventilation: 50%
lighting: 40%
cooling: -60%
The only explanations we can think of for the bad result in cooling is: 1st: the fully glazed facade and 2nd: the server rooms which make up 45% of the total cooling energy.
We expected the building to achieve a better score since the ASHRAE standard is 10 years old and the standard the building adheres to is from 2016. Apart from that the COP of the chillers are slightly better than the ones demanded in the mandatory provisions.