You are partially correct.
You are assuming that the basement is also air-conditioned to 27°C. This is not normally the case. The slab program does not have a basement.
The 2°C rule is for the input of an unknown temperature surface, the upper surface of the slab model, which is covered by the building floor..
This number does not apply to the basement wall temperature, as the later is calculated by the basement program.
There may be a 2°C difference in temperature across the basement wall. However, this value is calculated by simulation, and therefore need not be assumed.
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: ooi_kb3@xxxxxxxxxxx
Date: Tue, 15 Feb 2011 02:19:16 +0000
Subject: [EnergyPlus_Support] Re: Ground Temperature: Building Surface
i believe that the purpose of the ground heat transfer (basement or slab) programs is to get a more accurate (3-D) computation of the heat transferred from conditoned indoors. Once the indoor air is conditioned, all the time, the temperature on the outside face of the slab or basement will be about 2C less than the indoors. ooi
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "jipp06" <jippnojunk@...> wrote:
>
> Dr. Li,
>
> I don't get this -2*C rule. Take a basement zone with R20 wall insulation and indoor heating temperature of 27*C. I cannot imagine that the ground surface temperature would be the same as a non insulated basement with 17*C indoor temperature.
> Unless there are some things I don't understand. (I must admit that it does happen :) )
>
> Are you familiar with the basement and slab preprocessor programs? Could someone comment my understanding and fill the gaps. It would be apreciated.
>
> Quoted: "I have never done it but here is my understanding.
> add a GroundHeatTransfer:Control object to run the preprocessor. It will calculate the ground temperatures to use from the climate file you spécified. Get the results in the .SLAB or .BSMT file and enter those results in the relevent ground temp objects."
>
> Thx
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, YuanLu Li <yli006@> wrote:
> >
> >
> > What could be a probable default ground temperature for Indian climates, say New Delhi or Jaipur?
> >
> > It does not matter where you are, the deep earth temperature is maintained by the ice at the poles and the sea water current. It will be in the range between 18 to 22�C. If you go deeper, the earth temperature would increase.
> >
> > The surface ground temperature below the building is a value between this deep ground and the undisturned surface grouond temperature, which varies with the daily outdoor air temperature and the solar radiation on the surface.
> >
> > If you have a small building with no shade outside, the ground surface temperature under the building will follow the surface ground temperature not covered by the building via horizontal conduction. The slab and basement program will help you to make this calculation.
> >
> > When the building is air-conditioned to say 27�C, you assume 27 - 2 = 25 as the temperature below the building. This is reasonable.
> >
> > For an un-conditioned ground floor zone in the middle of a building, the ground cools the zone in Summer and heats the zone in Winter.
> >
> > To keep the basement temperature above zero in Winter, the basement wall need to be insulated to a depth of 1 meter below the ground surface and part of the ceiling up to one meter from the external wall. (The frost line)
> >
> > New Delhi is not near the sea, so you may need a higher value. The general guide is two degree less than the monthly average of the daily available. Without looking at the .stat file, my guess is 22 to 24 degree as the suitable under building ground temperature for your location..
> >
> > I am using 25�C for Singapore. 20 to 22 degree C (Monthly average) for Toronto, Canada.
> >
> > What you need to do is to measure a few basement floor temperature at night (3 to 5 am) to confirm that the number chosen is reasonable.
> >
> > If you are doing detailed daily experiment on the building, you would need the exact value, and some observation on the soil moisture condition (diffusivity). For the annual energy usage calculation, a monthly average value is good enough.
> >
> > Dr. Li
> >
> >
> >
> >
> >
> > To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> > From: jippnojunk@
> > Date: Sat, 12 Feb 2011 20:39:03 +0000
> > Subject: [EnergyPlus_Support] Re: Ground Temperature: Building Surface
> >
> >
> >
> >
> >
> >
> > Why don't you just use the technique described in the documentation?
> >
> > OK. I have reread the section in I/O manual.
> > "GroundHeatTransfer:Control
> > The GroundHeatTransfer:Control object determines if the Slab and Basement preprocessors are going to be executed. When a Slab or Basement run is performed the results are saved in files with extensions .SLAB or .BSMT so that they do not need to be rerun if no input changes are made to the GroundHeatTransfer:Slab or GroundHeatTransfer:Basement objects."
> >
> > I have never done it but here is my understanding.
> > add a GroundHeatTransfer:Control object to run the preprocessor. It will calculate the ground temperatures to use from the climate file you spécified. Get the results in the .SLAB or .BSMT file and enter those results in the relevent ground temp objects.
> >
> > Let me know it that does it.
> > I am learning as well.
> > Cheers.
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Tony David <tony.energie@> wrote:
> > >
> > > Hi everyone
> > > �
> > > The Energy plus documentation specifies that for typical commercial buildings in the USA, a reasonable default value for ground temperature: building surface�is 2C less than the average indoor space temperature.
> > > What could be a probable default ground temperature�for Indian climates, say New Delhi or Jaipur?
> > > �
> > > Thanks
> > > Tony
> > > MREL
> > > �
> > > �
> > >
> >
>
--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "jipp06" <jippnojunk@...> wrote:
>
> Dr. Li,
>
> I don't get this -2*C rule. Take a basement zone with R20 wall insulation and indoor heating temperature of 27*C. I cannot imagine that the ground surface temperature would be the same as a non insulated basement with 17*C indoor temperature.
> Unless there are some things I don't understand. (I must admit that it does happen :) )
>
> Are you familiar with the basement and slab preprocessor programs? Could someone comment my understanding and fill the gaps. It would be apreciated.
>
> Quoted: "I have never done it but here is my understanding.
> add a GroundHeatTransfer:Control object to run the preprocessor. It will calculate the ground temperatures to use from the climate file you spécified. Get the results in the .SLAB or .BSMT file and enter those results in the relevent ground temp objects."
>
> Thx
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, YuanLu Li <yli006@> wrote:
> >
> >
> > What could be a probable default ground temperature for Indian climates, say New Delhi or Jaipur?
> >
> > It does not matter where you are, the deep earth temperature is maintained by the ice at the poles and the sea water current. It will be in the range between 18 to 22�C. If you go deeper, the earth temperature would increase.
> >
> > The surface ground temperature below the building is a value between this deep ground and the undisturned surface grouond temperature, which varies with the daily outdoor air temperature and the solar radiation on the surface.
> >
> > If you have a small building with no shade outside, the ground surface temperature under the building will follow the surface ground temperature not covered by the building via horizontal conduction. The slab and basement program will help you to make this calculation.
> >
> > When the building is air-conditioned to say 27�C, you assume 27 - 2 = 25 as the temperature below the building. This is reasonable.
> >
> > For an un-conditioned ground floor zone in the middle of a building, the ground cools the zone in Summer and heats the zone in Winter.
> >
> > To keep the basement temperature above zero in Winter, the basement wall need to be insulated to a depth of 1 meter below the ground surface and part of the ceiling up to one meter from the external wall. (The frost line)
> >
> > New Delhi is not near the sea, so you may need a higher value. The general guide is two degree less than the monthly average of the daily available. Without looking at the .stat file, my guess is 22 to 24 degree as the suitable under building ground temperature for your location..
> >
> > I am using 25�C for Singapore. 20 to 22 degree C (Monthly average) for Toronto, Canada.
> >
> > What you need to do is to measure a few basement floor temperature at night (3 to 5 am) to confirm that the number chosen is reasonable.
> >
> > If you are doing detailed daily experiment on the building, you would need the exact value, and some observation on the soil moisture condition (diffusivity). For the annual energy usage calculation, a monthly average value is good enough.
> >
> > Dr. Li
> >
> >
> >
> >
> >
> > To: EnergyPlus_Support@xxxxxxxxxxxxxxx
> > From: jippnojunk@
> > Date: Sat, 12 Feb 2011 20:39:03 +0000
> > Subject: [EnergyPlus_Support] Re: Ground Temperature: Building Surface
> >
> >
> >
> >
> >
> >
> > Why don't you just use the technique described in the documentation?
> >
> > OK. I have reread the section in I/O manual.
> > "GroundHeatTransfer:Control
> > The GroundHeatTransfer:Control object determines if the Slab and Basement preprocessors are going to be executed. When a Slab or Basement run is performed the results are saved in files with extensions .SLAB or .BSMT so that they do not need to be rerun if no input changes are made to the GroundHeatTransfer:Slab or GroundHeatTransfer:Basement objects."
> >
> > I have never done it but here is my understanding.
> > add a GroundHeatTransfer:Control object to run the preprocessor. It will calculate the ground temperatures to use from the climate file you spécified. Get the results in the .SLAB or .BSMT file and enter those results in the relevent ground temp objects.
> >
> > Let me know it that does it.
> > I am learning as well.
> > Cheers.
> >
> > --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Tony David <tony.energie@> wrote:
> > >
> > > Hi everyone
> > > �
> > > The Energy plus documentation specifies that for typical commercial buildings in the USA, a reasonable default value for ground temperature: building surface�is 2C less than the average indoor space temperature.
> > > What could be a probable default ground temperature�for Indian climates, say New Delhi or Jaipur?
> > > �
> > > Thanks
> > > Tony
> > > MREL
> > > �
> > > �
> > >
> >
>
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