Split system DX systems always have difficulty controlling humidity; the thermostat senses only temperature in most cases. In addition, the cooling coil is not designed or intended for high latent loads (generally a sensible heat ratio of ~0.7 is expected). The fact that the compressor cycles on and off compounds the humidity control problems, since no humidity gets removed during an "off" cycle. In fact, moisture on the cooling coil can even get re-absorbed if the fan continues to operate while the compressor is off.
Your system gets sized by E+ according to sensible load, not latent load. When you reduce the sensible load, but latent loads remain unchanged, the space humidity will rise because the DX coil (correctly) canot handle the higher sensible heat ratio.
If a split system is a logical choice for your application, then the savings you are seeing may be realistic. If you want to deterime the "maximum possible" savings in your , I think you should consider a cooling system which modulates the cooling (no compressor cycling on and off). That should control humidity much better.
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "aymericnovel" <aymericnovel@...> wrote: > > Hi, > I have simulated a 90m² apartment in HoChiMin, vietnam. This is my > first study in such a humid climate so I apologize if my question is > trivial. Here is my problem: > > I use the SingleSpeed DX coil in each cooled zone to simulate a split > system. > It recirculates only room air. The temperature setpoint for zone is > 26°C. > My study aimed to quantify benefits on cooling energy consumption of > actions on the envelope (use of insulating concrete, low SµHGC > windows) and reduction of lighting related internal loads. So far, > very logical. > > And logically, I found that my sensible loads are reduced (about 30%). > > But, the DXCoil adapts to a lower sensible load by blowing less air > at the same temperature. For an idea here are the 2 configuration at > the air outlet of the coil: > High sensible load => 0.08kg/s at about 13.5°C > Low sensible load => 0.05kg/s at 13.5°C > > Logically, in the second case, the sensible cooling rate delivered is > smaller, according to the fact sensible load is indeed smaller. > BUT, the latent load increases accordingly. The SHR (Sensible Heat > Ratio) decreases in the second case, making the latent part bigger: > High sensible load => SHR = 0.7 > Low sensible load => SHR = 0.6 > > So, when looking at the result on the total cooling rate, it is not > as fruitful as expected...I guess it is a known fact for engineers > who are used to work with high outdoor humidity ratio > > Is it because the coil is "single speed" that the regulation is > automatically made by airflowrate? Is there a way to modify the blown > air temperature instead? Indeed, that would create energy savings > also on the latent part to blow the same airflow rate at a higher > temperature if sensible load is increased? Isn't that the tendency > of current evaporator to increase SHR? Should I change the object I > use? I guess it is all related to "how the object calculates the > blown air temperature"... > > If somebody could help me clear my mind on this topic, I would be > grateful! > > Tnaks a lot, > Aymeric >