Pump Electric Consumption of Primary/Secondary Hot Water Loop

I would like to simulate a primary/secondary hot water loop.

All the flow rates are autosize, the pump head for both primary and secondary loop are 60ft. There is just one boiler and I don't set up the pump stage. Primary pump is constant speed while secondary pump is variable.

I checked the "Pump Electric Energy" after the annual simulation and expected that the MAXIMUM pump electric energy of the secondary loop would not be huge different from primary loop, maybe half of it or something similar. However, that number was just 1% of primary loop electric consumption which I think is totally unreasonable.

Anyone has similar experience before? Is it because I didn't set up the pump stage?

Depending on what you're modeling it may be reasonable. It really depends on the loads that are being imposed on the secondary loop. I would recommend first investigating whether the autosized flow rates are reasonable, not just the annual energy usage values. The head for secondary pumps is usually considerably higher than the primary pumps. The flows should be similar though.

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Lincoln

answered 2015-12-18 10:57:14 -0500

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I set up the rated flow rate for primary and secondary HW pump, it seems that the flow rate of primary loop is always at the max number (rated flow rate), even in summer. Is there something wrong?

Yan (2015-12-20 12:07:55 -0500) edit

How many chillers do you have? Are the primary pump(s) constant speed or variable speed?

Lincoln (2015-12-21 09:24:44 -0500) edit

I have 3 chillers and 3 boilers. Primary pumps are constant speed and secondary pumps are variable

Yan (2015-12-21 09:44:41 -0500) edit

I did a few tests this this morning. It seems it is the water use fixture which causes the problem, but don't know how to deal with it appropriately. In this case, domestic hot water is served by hot water loop. I connected the water use fixture to the secondary HW loop, but primary HW loop keeps running during the whole year. After I delete the water use fixture, the primary pumps profile looks better. Secondary pumps still consume much less energy than primary pumps, though.

Yan (2015-12-21 09:49:43 -0500) edit

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Pump Electric Consumption of Primary/Secondary Hot Water Loop

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Pump Electric Consumption of Primary/Secondary Hot Water Loop