We are undergoing energy model calculation in e+ to meet LEED's mandatory requirement. Our new construction will be a medical office and lab conditioned with VRF system complemented by independent Outdoor Air Units (OAU) to meet IAQ requirement. This OAU consists of supply and exhaust fans only (no coils, mixers, or exchangers). The result of this combination is a huge amount of unmet hours (up to 3700 hours a year). Therefore in e+, it is also possible to introduce OA without adding independent OAU by using mixer embedded inside VRF's Terminal Units. When I implemented this (both cooling and OA provision only through VRF Terminal Units), with the exact technical specifications and the same amount of outdoor air provisions, there was no unmet hours problem occurred (only around 30 hours a year). How this could be happened? Logically, it would behave similar with the OAU equipped. Or maybe I missed something?
For additional information, our project location is in tropical humid climate, Surabaya-Indonesia. Most of the equipment were autosized. The two and only defined input were just the rated COP of each condensor and the volume flow rate (debit) of outdoor air required in each zone. This is because we are still collecting technical information from our MEP team, this is not an easy task since this is new to us and we are not used to in terms of documenting details needed by LEED.
I have asked about this topic in another forum, and experts there suggested that I utilize ZoneInfiltration:DesignFlowRate to take into account ventilation loads from OA units since autosizing in EPlus does not include this type of load as thermal and envelope loads does, leads to undersizing and lots of unmet hours. Nevertheless, when I examined the infiltration + VRF result, it showed far higher Cooling Electricity End Use compared to when I used OA mixer inside VRF TU (811 to 622 GJ). Even though they both have similar amount of OA volume flow rate (m3/s) introduced into the zones (109 conditioned and 26 mech vented zones). My conclusion, I don't think that this method would solve my case since unmet hours are still appeared (700 hours). Any suggestion?
Additionaly, I was told that EPlus team is trying to solve this in their future version of EPlus. Anyone knows how long will it be?
Regards,
Ade