Re: [EnergyPlus_Support] Re: Why Autosize does not consider System Outdoor Air Loads

It will work as long as the supply air temperature in hte sizing:zone object can combat the zone load (so for heating it must be more than the zone heating setpoint, and for cooling less than the zone cooling setpoint). In your sizing:system object you set the design supply air temperature as what you expect the air side system to bring (that excludes fancoils which are not system equipment, but zone equipment).The ADU sizing routine has a flag that will properly size the ADU on ventilation rate if the sizing:system object uses ventilation rate as the sizing method, otherwise it is sized from the information from the sizing:zone object.

2014-07-07 15:41 GMT+02:00 HJ wanghaojie630@xxxxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx>:

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Thanks Jean. So for example, if I have heating setpoint of 20C. My DOAS is supplying 13 C and the sizing:system is also set as 13 C for central heating, but the sizing:zone heating supply air temperature is set as 30C. Will it properly size the system? The problem is that I have radiant system but the only place I can specify the water temperature is in sizing:plant. From theÂ EnergyPlus engineering reference, it says the sizing:zone will perform first to calculate how much air flow needed based on supply air temperature (specified in sizing:zone) and zone load. Then sizing:system will run to calculate the air system side. Then sizing:plant will run to calculate the plant water flow rate. However, based on this sequence, I think it will not work properly for radiant system. Or maybe they use different procedure for radiant system?

Thanks,

HJ

On 7/4/2014 1:06 AM, 'jeannieboef@xxxxxxxxx' jeannieboef@xxxxxxxxx [EnergyPlus_Support] wrote:

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Hi Karen, as soon as you posted this, I went to test it, because it messes up my current understanding of the autosizing in e+. For GermÃ n's case, it does not work and fits my current mental model. For HJ's case, it would work as long as the zone setpoint is able to be corrected by the system's air supply. So if he has a zone heating setpoint of 20 and is trying to heat with 13 C system supply air, it will not size the equipment properly and the issue is the same as GermÃ n's. Â

Mit freundlichen GrÃ¼Ã?en- Sent from my iPhoneÂ (excuse the brevity)

i. A.

Jean Marais

b.i.g. bechtold

Tel. Â +49 30 6706662-23

On 03.07.2014, at 23:53, "Karen Walkerman kwalkerman@xxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:

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I think that you might not be setting the design heating and cooling supply air temperatures correctly in the Sizing:System object. If you have an air handler providing unconditional ventilation air to zones, set the design heating temperature equal to the outdoor temperature of your heating design day at the system level. Same with cooling. Then your ZoneHVAC equipment should size correctly.

Karen

On Jul 3, 2014 12:30 PM, "HJ wanghaojie630@xxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:

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Thanks. I misspoke, actually s1 provide 13 air temperature all time. So in summer it provide some cooling, and winter it preheat air to 13 C. In this case, will s2 be oversized for summer and undersized for winter?

HJ

On 7/3/2014 12:16 PM, ecoeficiente@xxxxxxxxx [EnergyPlus_Support] wrote:

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In your case, s2 will only be sized for zone loads without accounting for s1 ventilation load. But, as you say, your s1 system provides neutral air temperature, that is, no load. In that case you do not have the problem I mentioned.

Regards.