Question for anyone who uses Elite Chvac.

[Light9]

Hey guys

I have 2 questions concerning Elite, the first question is:

When I drop the humidity of the air below a certain point, reheat coil should be added in order to reheat the air to maintain the sens zone temperature. A program like HAP does this automatically and it adds a heating coil and gives you it's capacity. I have noticed that Elite doesn't do this. You can drop the humidity all you want and it won't add a reheat coil and won't even adjust the cooling coil temperature. Am I missing something here?

My second question is: I noticed that Elite doesn't consider the supply fan sens loss during the winter, only during the summer. This is wrong, isn't it? The supply fan should be considered a sens gain during the summer and sens loss during the winter?

Thanks in advance.

 

[Drazen]

I used at least half dozen of calculation software and don't like much those who try to do work for you, in more complex projects such automatism can cause nasty errors.

Maybe I am becoming too "old school", but sometimes on these forums try to sharply point out to young engineers to not expect software packages to do design work for you. Over the globe I see young engineers who just press buttons, and when troubles come in, they try to blame software. Such approach works only in areas where engineer's responsibilities are not defined. Other than that, all software manufacturers have clear accountability waivers, and engineering chambers also mention that often.

At best, software is your reliable helper who does less errors in tedious tasks. You have to save "clever" work for yourself.

Chvac does give you overview of all loads in good manner. You can calculate reheat in Elite psychro module and add it to chvac air system. In some other packages I used to use psychro module is also separate. not only automatic additions, but hap also has their unique optimization algorhythm for block loads. you can accept it or not, but you won't get their algorhythm for your own review. that is why i use hap mostly in less formal calculations.

as regards to fan heat addition, for decades internal gains were not being added for heat loss calculations. they are currently used for yearly-energy calculations, but i did not hear that any of heat loss calculation standard adopted such approach.

do not mix energy consumption modelling with heat loss and gain calculation, these are two distinct calculations!

 

[Light9]

Thanks for your answer but let me elaborate more about the fan load.

This is a picture of a HAP report, as you can see, HAP does subtract the fan load when it comes to heating during the winter

http://files.engineering.com/getfil...-4d0f-9ea7-c85a6297f964&file=Fan_Load_HAP.jpg

And this is a picture of an Elite report for the same AHU

http://files.engineering.com/getfil...703-b2e9-2f44b037de4a&file=Fan_Load_Elite.jpg

I just want to know which is right. Why does HAP subtract the supply fan load and Elite doesn't?

Thanks in advance.

 

[Drazen]

Ok, this is for ventilation loads which i did not think of in previous post.

What did you put in "motor efficiency" or something like that in air handler settings screen in chvac?

it seems like efficiency put is 80%, meaning 20% goes to air stream. am i correct?

 

[Light9]

70% efficiency in both HAP and Elite. Any ideas?

 

[Drazen]

A load is a load. Fan adding heat to supply air is not adding load but actually reducing it. Sofware likely does not reduce loads but only adds it. So if nothing is to be added on fan column, it simply puts zero, as calculation algorithm likely does not have subtraction at that column. Title "Fan and Duct Loads" is somewhat misleading, it should probably be written something like "Duct loads in winter" and "Fan and Duct Loads in summer", but so many words would not fit in the report layout.

As mentioned above, most peak heating loads calculations do not subtract loads from fan or internal gains - for reasons of safety margin. It is very "modern" concept, and I don't know if any standard supports it. Energy consumption calculations are different and they do subtract internal loads regularly.

HAP has their own agenda. They do not car about official standards much. You should study HAP help and manual to see how they formally explain that. I will try to look at it when reaching HAP.

 

[Light9]

Thanks a lot for your replies, Drazen. I have learnt a great deal.

So in closing, in your opinion, should I manually subtract the fan load during the winter or at least, reduce it slightly by say 50% or so? or just leave it as is?

 

[Drazen]

I always leave it, i.e. I never subtract internal heat gains from heat loss calculation.