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[EnergyPlus_Support] Re: Manual HVAC Sizing Error
Jean,
Nearly. Under HVACSizingSummary E+ produces the HVAC sizing in kW for each zone. Sum the sizes for a tenancy and you have the required heating or cooling HVAC size. It's this that we have been given from our consultant that we need to be able to vary.
Just a brief note to thank you for your assistance with regards to this. In playing around with the E+ .idf I have found my solution. Under HVAC Design Objects in the .idf there are two inputs - Sizing:Parameters and Sizing:Zone. Sizing:Parameters, with a default of 1.2 looks to oversize the HVAC by 20%. It works on a global HVAC setting. Sizing:Zone does the same thing on a zone basis. So if you set it at 1.0 you get a certain sized HVAC for the zone and if you set it to 2.0 it doubles the size. I adjusted these zone sizings to get the HVAC for my tenancy to be that specified by the consultant. So E+ is essentially providing a conditioned space with an oversized HVAC and as such, the equipment will be operating far from optimum - that is to say working at <100% on the part load curves.
I have taken many of your ideas and implemented them to minimise the errors we get, and certainly your descriptions have improved my working knowledge of how E+ works. Thank you for this.
Regards,
Andrew Bell
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "jeannieboef" <jeannieboef@...> wrote:
>
> I'm guessing that you wanted to tell the equipment, "you have a zone cooling capacity of 40 W/m^2" and the equipment is not delivering said cooling. Default e+ fans will only cycle on and off to meet the loads in the space and if they've been autosized they will not deliver more than what was nessecary to meet the loads that were there on your design day.
>
> Make sure your fans are set to continous, i.e. fan object is FAN:CONSTANTVOLUME. I think the fan:variable volume will work like the Fan:OnOff only to meet space loads/ventilation requirements.
>
> Ideally you also manually specify all the fan parameters, but this might mean that it does not match your coil and may cause more errors than it solves. If you must use variable volume fans you'll need to specify a matrix of curve coeff. for different speeds (see inputoutput reference guide). The are also help excel sheets in the eplus support web page for this I believe.
>
> But if you are more after an idea of how your space performs you could use an ideal air simulation (simple HVAC in Design Builder) where you only specify the AHU air temperature and volume in, and combine it with a negative "process load" for which you can also specify the latent fraction.
>
>
>
> This componant based software
>
> That's because the
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "energy.partners" <energy.partners@> wrote:
> >
> > Jean,
> >
> > Thanks so much for your assistance regarding this - we really do have ourselves in a pickle with our Client wanting to submit their building proposal before Christmas and we're quite a bit out of our depth here.
> >
> > You suggestions have worked regarding setting the sizes of the zone (cooling) coils. Our HVAC designer has sent us the sizing of the HVAC equipment and as much as we fiddle E+ still spits out the same HVAC sizing, with the coils sizes as per our input. We suspect the designer has oversized the equipment as it is almost twice the size that E+ calculates but that's OK. But we'd like to input this specified sized equipment.
> >
> > Regards,
> >
> > Andrew Bell
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "jeannieboef" <jeannieboef@> wrote:
> > >
> > > you'll find that at a delivery air temperature of 22 degrees, you won't achieve much more than 2 W/m2 of cooling at normal room air change rates lower than 4 ach. So either increase the air flow rates tremendeously or decrease the "off-coil" temperature or delivery temperature to something more in the lines of a standard fan-coil, say 14 degrees C. The default sensible heat removal ratio for your problem coil may also be adjusted, meaning you say that more heat is removed in the condensing or latent heat removal potencial of your coil.
> > >
> > > Do is this cooling coil in your central AHU or in a zone equipment?
> > >
> >
>
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