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About to replace ASHP with GSHP

Last Post 23 Jan 2010 12:36 PM by 1FloridaNative. 21 Replies.

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engineer

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Posts:2749

23 Jan 2010 08:02 AM
Jim, A properly designed closed loop delivers EWT at +/- 20 of deep ground temp. Around here (Jacksonville) that takes upwards of 300' per ton, which amounts to a very pricey closed loop installation. I'm quite skeptical of a claim of 74-88 EWT at end of cooling season. I'd want to see that backed up by loop design software. Once EWT gets much above 90, the system will run no more efficiently than an ASHP, but at much higher first cost. In FL we don't have really really hot weather, design temps run in the low 90s, but it persists for months on end, and we have high latent loads making sizing vital for comfort. In your shoes, with the Floridan aquifer available at 85' I'd lean toward a 2 well pump and reinject system with provision for isolating and flushing the unit heat exchanger. Space the two wells as widely as practical to prevent thermal short circuiting. More info I'd want: 1) Test aquifer water for hardness etc. WF literature lists maximums for about 10 parameters 2) Actual water temp from aquifer. 72 may be optimistic; 74-75 may be closer 3) Assurance that a pump can be properly selected and sized for your situation - aquifer water standing at -10', well above shallow water table is not surprising - typical of the Floridan. An ill-informed pump selection would gobble up any savings from a carefully selected WSHP. Above all, don't cave in to the advice to oversize. You'll be much more comfortable year round if you get this right. email me at "waterleo 'at' comcast 'dot' net" if you'd like to discuss options. Tampa's too far for me to take on an install, but a consulting role is possible.

Curt Kinder <br><br> The truth is incontrovertible. Malice may attack it, ignorance may deride it, but in the end, there it is - Winston Churchill <br><br><a href="http://www.greenersolutionsair.com">www.greenersolutionsair.com</a>

1FloridaNative User is Offline

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Posts:20

23 Jan 2010 12:36 PM
Posted By engineer on 01/23/2010 8:02 AM Jim, A properly designed closed loop delivers EWT at +/- 20 of deep ground temp. Around here (Jacksonville) that takes upwards of 300' per ton, which amounts to a very pricey closed loop installation. I'm quite skeptical of a claim of 74-88 EWT at end of cooling season. I'd want to see that backed up by loop design software. Once EWT gets much above 90, the system will run no more efficiently than an ASHP, but at much higher first cost. In FL we don't have really really hot weather, design temps run in the low 90s, but it persists for months on end, and we have high latent loads making sizing vital for comfort. In your shoes, with the Floridan aquifer available at 85' I'd lean toward a 2 well pump and reinject system with provision for isolating and flushing the unit heat exchanger. Space the two wells as widely as practical to prevent thermal short circuiting. More info I'd want: 1) Test aquifer water for hardness etc. WF literature lists maximums for about 10 parameters [i]I found a water quality section for WF commercial (7-25 ton)[/i] [i]with the limits for over a dozen conditions by copper and cupro-nickel exhange unit. [/i] [u][i]Where does one go to have your sample tested for these items? [/i][/u] 2) Actual water temp from aquifer. 72 may be optimistic; 74-75 may be closer [i]72 is just a number I've heard around the springs. I'll measure my well this weekend. 90 degree EWT was mentioned as a break even with ASHP, so [u]would 75 vs 72 temperature from my well make a big difference?[/u] Measured well water temperature and was surprised to find that it was just below 76 degrees. I had always read that our aquifer water was consistently between 66 degrees and 70 degrees. My well must not be in that aquifer, bummer. [/i] 3) Assurance that a pump can be properly selected and sized for your situation - aquifer water standing at -10', well above shallow water table is not surprising - typical of the Floridan. An ill-informed pump selection would gobble up any savings from a carefully selected WSHP. [i]I agree with critical decision of pump selection. I would be looking at a new source well, with right pump for GWHP, and use my existing well as the dump and irrigation source. I have some concern about the dumping of whatever gets used to dissolve scale, but I would think it would be simple to control with valves to divert flow from dump well during this maintenance. [u]Any pointers on selecting the right pump?[/u] [/i] Above all, don't cave in to the advice to oversize. You'll be much more comfortable year round if you get this right. [i] Agree most emphatically. I even looked at upgrade to insulation, tightening up air leaks (sliders are so pourous) to reduce load (59,000 btu/hr) but didn't think I could get down to two Envision 026 units, so a multistage Envision 038 for the main house zone and an 026 for the rooms served by the unit in addition seems reasonable[/i]. [/quote] Edit on 01/25/2010 to add water temperature measurement.