[Equest-users] Heat recovery working too well?

[Adam Barker]

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<mailto:abarker at pemi.com>

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