[Equest-users] Heat recovery working too well?

Daniel Knapp danielk at arborus.ca
Thu May 28 12:02:51 PDT 2015

Hmm, I would be careful about using the LS-D reports in this way. The OA load is not precisely equal to the SS-D energy minus the LS-D energy. The miscellaneous and lighting loads also need to be considered, and it is important to remember that in zones with baseboards, the heating load will be met by the baseboards first and then the system. In addition, the LS-D reports are calculated in advance of the systems calculations assuming constant zone temperatures. Corrections to this calculation are made by the systems calculations. 

If you are unsure about the results, you might want to try varying the outdoor air flow rates, the effectiveness, and the effective R-value of the envelope to see if the results you are getting make sense. You could also try limiting the calculation to a single day in January and doing some hand calculations of the envelope and OA loads to see if the results are making sense. I recommend looking at the ERV reports as well, they tend to give a fair bit of information about the energy savings from energy recovery alone. 

Hope that helps,

Daniel Knapp, PhD, PPhys, LEED® AP O+M
danielk at arborus.ca

Arborus Consulting
Energy Strategies for the Built Environment
76 Chamberlain Avenue 
Ottawa, ON, K1S 1V9 
Phone: (613) 234-7178 ext. 113
Fax: (613) 234-0740

> On May 28, 2015, at 2:22 PM, Adam Barker <ABarker at pemi.com> wrote:
> Has anyone else come across heat recovery giving very good results in their model that are higher than expected. In a heating dominated climate, we have a PSZ system serving 5 zones, with baseboards used to meet heating loads in the slave zones (they’ve been hard sized to just get the unmet hours in an acceptable range). 
> I have broken down an analysis of building heating energy by month, from LS-D and SS-D.  Assuming the SS-D account for all ‘building’ loads (envelope, infiltration, lights, etc), and SS-D is all that, plus the OA load.  For a 50% effective  ERV (and no additional fan heat), I get the following for winter months:
> Monthly Heating Energy Used (MBTU)
> Envelope Loads (LS-D) no ERV
> Envelope and OA energy (SS-D) no ERV
> Envelope and OA energy (SS-D) with ERV
> Envelope energy as % of total (LS-D/SS-D) no ERV
> Reduction of energy in SS-D due to ERV (at 50% eff)
> J
> 126
> 222
> 154
> 0.5676
> 0.306
> F
> 112
> 196
> 135
> 0.5714
> 0.311
> M
> 90
> 157
> 101
> 0.5732
> 0.357
> A
> 54
> 82
> 47
> 0.6585
> 0.427
> O
> 37
> 52
> 27
> 0.7115
> 0.481
> N
> 67
> 112
> 70
> 0.5982
> 0.375
> D
> 108
> 187
> 127
> 0.5775
> 0.321
> E.g. in January a 50% eff ERV gives a 30% reduction in heating energy, even though the ‘building’ pre-OA accounts for 55% of the total energy. My gut feeling is that the 55% is not accurate and it is actually lower, but I can’t convince myself using the reports.
> Fiddling with the heat recovery control schemes doesn’t seem to change the heating results by much either, however changing the effectiveness has a big impact to the results. In comparison, improving the wall performance has a relatively small impact.
> I should say that this is a preliminary model so no design drawings available, and it a retail space with about 0.18 cfm OA/sqft.
> Adam Barker, MBSc, C.E.T., LEED AP BD+C
> Energy Project Manager
> Provident Energy Management Inc.
> T: 416-736-0630 x 1874 | abarker at pemi.com
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