[Bldg-sim] Bldg-sim Digest, Vol 66, Issue 22

Jason Quinn jason.e.quinn at gmail.com
Mon May 27 16:53:21 PDT 2013


If your going to use the coefficient method you shouldn't use 1/20th of the
ACH50 as the base infiltration. It is supposed to be an average value for
typical exposure etc. You could use the BLAST eqn but you will need to
adjust the inputs. I'd suggest looking at the pressure drop across the
house at the peak wind condition and see what the Pa difference is across
the windward and leeward walls. Assume a linear drop with pressure from
your ACH50 value and pull out the "basic infiltration" from that.

I agree that 1ACH at 50Pa is challenging with standard practice construction.
The average new home in NZ without anything special is about
6ACH at 50Pa.That said, two weeks ago, I witnessed a blower door test of
a passive house
(1st time builder) that was less than 0.3ACH at 50Pa the first time we turned
on the blower door. This was the first time this builder had attempted an
"airtight" house - after fixing a few oversights it was at
0.26ACH at 50Pa.The structure was designed to be sealed properly and he
used ProClima's
tapes and membranes. If you build  a SIP house it is also likely to be
under 1ACH50 without trying too hard.


Jason Quinn
+64 21 1846 911


On Tue, May 28, 2013 at 8:00 AM, <bldg-sim-request at lists.onebuilding.org>wrote:

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> Today's Topics:
>
>    1. Modelling Infiltration for Low Energy Houses (Hayes Zirnhelt)
>    2. Re: Modelling Infiltration for Low Energy Houses (Shaun Martin)
>
>
> ---------- Forwarded message ----------
> From: Hayes Zirnhelt <hzirnhelt at hotmail.com>
> To: "bldg-sim at lists.onebuilding.org" <bldg-sim at lists.onebuilding.org>
> Cc:
> Date: Mon, 27 May 2013 09:40:13 -0700
> Subject: [Bldg-sim] Modelling Infiltration for Low Energy Houses
> Hi,
>
> I've created a detailed multi-zone model of a low energy home in Canada in
> EnergyPlus. I am looking at the peak heating load results and finding that
> the infiltration predicted seems quite high. I'd be interested to hear how
> other building modellers are approaching infiltration, and any general
> thoughts anyone has on this situation.
>
> The model is based on the design - the house has not been constructed yet,
> but it is assumed that an ACH at 50pa rating of 1 can be achieved.
> EnergyPlus has a simple infiltration modelling option, where the air
> leakage can be input as ACH@ regular pressure (I've assumed this is equal
> to 1/20 = 0.05).
>
> EnergyPlus's basic infiltration model can adjust the infiltration rate for
> delta T and windspeed, using the following formula:
>
> Infiltration = I_design * {A + B (T_zone - T_outdoor) + C*windspeed +
> D*windspeed^2 }****
>
> ** **
>
> The big question I have is what coefficients should be used? EPlus
> provides three suggestions:
>
>
> 1. coefficients from BLAST:
>
>
> A =     0.606,                   !- Constant Term Coefficient****
>
> B =     0.03636,                 !- Temperature Term Coefficient****
>
> C =    0.1177,                  !- Velocity Term Coefficient****
>
> D =    0;                       !- Velocity Squared Term Coefficient
>
>
> 2. coeffs from DOE: 0, 0, 0.224 (windpeed), 0
>
>
> 3.Default: 1,0,0,0 which means a constant ACH with no modification.
>
>
> The BLAST coefficients seemed to be the best to me because I think wind
> and temperature difference should be accounted for and there should always
> be some basic infiltration. However, using these coefficients at the peak
> heating load condition (delta T ~ 40C, windpeed = 27 km/hr) the
> infiltration rate is tripled from the base 0.05 ACH, and the total load
> from infiltration equals 2.2 kW, which is the largest component of the
> heating load.
>
>
> For a relatively tight house this seems like an unrealistic value to me,
> but I do not have much to compare it against.
>
>
>
> Thanks,
>
>
> Hayes
>
>
> Hayes Zirnhelt, M.A.Sc****
>
> EcoOptimal Building Energy Analysis****
>
> hayes at eco-optimal.ca****
>
> www.eco-optimal.ca****
>
> T: 778.961.0086
>
>
>
> ---------- Forwarded message ----------
> From: "Shaun Martin" <smartin at shaunmartinconsulting.com>
> To: "'Hayes Zirnhelt'" <hzirnhelt at hotmail.com>, <
> bldg-sim at lists.onebuilding.org>
> Cc:
> Date: Mon, 27 May 2013 11:39:03 -0700
> Subject: Re: [Bldg-sim] Modelling Infiltration for Low Energy Houses
>
> Hi Hayes,****
>
> ** **
>
> The ZoneInfiltration:EffectiveLeakageArea approach in E+ might give you
> better results as it is tailored for residential buildings.  It accounts
> for stack, wind and sheltering better than the
> ZoneInfiltration:DesignFlowRate method, which is used more for larger
> building models.  ****
>
> ** **
>
> Regardless of the method, the bigger problem is the infiltration
> schedule.  You could start with the schedules they have in eQuest.   The
> operation of the HRV will affect the infiltration schedule.  And, on larger
> buildings, of course, infiltration in core zones can be set to zero.****
>
> ** **
>
> On a 600m3 house, ACH50 = 1.0 is roughly 166 L/s.  This is about 55 L/s at
> 10Pa,  and translates to an effective leakage area of about 0.45 cm/m2.
> These are what I would use as design numbers.   From experience, ACH50 =
> 1.0 (even 1.5) is a challenging target to reach and can’t be reached unless
> you use a blower door during construction.  ****
>
> ** **
>
> Hope this helps,****
>
> Shaun****
>
> ****
>
> ** **
>
> *From:* bldg-sim-bounces at lists.onebuilding.org [mailto:
> bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of *Hayes Zirnhelt
> *Sent:* Monday, May 27, 2013 9:40 AM
> *To:* bldg-sim at lists.onebuilding.org
> *Subject:* [Bldg-sim] Modelling Infiltration for Low Energy Houses****
>
> ** **
>
> Hi,****
>
> ** **
>
> I've created a detailed multi-zone model of a low energy home in Canada in
> EnergyPlus. I am looking at the peak heating load results and finding that
> the infiltration predicted seems quite high. I'd be interested to hear how
> other building modellers are approaching infiltration, and any general
> thoughts anyone has on this situation.****
>
> ** **
>
> The model is based on the design - the house has not been constructed yet,
> but it is assumed that an ACH at 50pa rating of 1 can be achieved.
> EnergyPlus has a simple infiltration modelling option, where the air
> leakage can be input as ACH@ regular pressure (I've assumed this is equal
> to 1/20 = 0.05).****
>
> ** **
>
> EnergyPlus's basic infiltration model can adjust the infiltration rate for
> delta T and windspeed, using the following formula:****
>
> ** **
>
> Infiltration = I_design * {A + B (T_zone - T_outdoor) + C*windspeed +
> D*windspeed^2 }****
>
>  ****
>
> The big question I have is what coefficients should be used? EPlus
> provides three suggestions: ****
>
> ** **
>
> 1. coefficients from BLAST:****
>
> ** **
>
> A =     0.606,                   !- Constant Term Coefficient****
>
> B =     0.03636,                 !- Temperature Term Coefficient****
>
> C =    0.1177,                  !- Velocity Term Coefficient****
>
> D =    0;                       !- Velocity Squared Term Coefficient****
>
> ** **
>
> 2. coeffs from DOE: 0, 0, 0.224 (windpeed), 0****
>
> ** **
>
> 3.Default: 1,0,0,0 which means a constant ACH with no modification.****
>
> ** **
>
> The BLAST coefficients seemed to be the best to me because I think wind
> and temperature difference should be accounted for and there should always
> be some basic infiltration. However, using these coefficients at the peak
> heating load condition (delta T ~ 40C, windpeed = 27 km/hr) the
> infiltration rate is tripled from the base 0.05 ACH, and the total load
> from infiltration equals 2.2 kW, which is the largest component of the
> heating load.****
>
> ** **
>
> For a relatively tight house this seems like an unrealistic value to me,
> but I do not have much to compare it against.****
>
> ** **
>
> ** **
>
> Thanks,****
>
> ** **
>
> Hayes****
>
> ** **
>
> Hayes Zirnhelt, M.A.Sc****
>
> EcoOptimal Building Energy Analysis****
>
> hayes at eco-optimal.ca****
>
> www.eco-optimal.ca****
>
> T: 778.961.0086****
>
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