[Equest-users] Boiler temperature for hybrid geothermal heat pump system

[Siliang Lu via Equest-users]

Hi Sharad,
 Thanks for your reply.
 My design is ambient geothermal heat pump system. The water loop
temperature ranges between 55-85F and the ground temperature is not so high
as 360-370F. What I am wondering is that if the boiler setpoint could be
much higher than ground heat exchanger setpoint if the size of boiler is
much smaller than that of GHX? Thanks a lot!

Have a great day!

All the best,
Siliang

Siliang

On Mon, Aug 8, 2016 at 5:46 AM, Sharad Kumar via Equest-users <
equest-users at lists.onebuilding.org> wrote:

> Hi Siliang,
>
> The Water loop set-point that you have got as may be 70 °F is the water
> temperature that is 21.11 °C.
>
> It is obvious to take set-point of the boiler below the Ground source HX
> as then it will operate.
>
> The ground source steam temperature may shoot up-to 360-370 °F.
>
> So may be taking steam boiler or steam plus hybrid boiler that is
> electricity and keeping the set-point from 180 to 230 °F can be a take.
>
> One can keep the set-point of the ground water heating loop as more than
> 230 °F to 370 °F may be 360 °F.
>
> Then the functioning will be okay.
>
> Generally the boiler set-point of electrical heater is 180 °F for steam
> water to 230 °F which is nearly 82 °C (180 °F ).
>
> *Thanks*,
> Sharad.
>
>
> ---------- Forwarded message ----------
> From: Siliang Lu via Equest-users <equest-users at lists.onebuilding.org>
> To: "equest-users at lists.onebuilding.org" <equest-users at lists.onebuildin
> g.org>
> Cc:
> Date: Sat, 6 Aug 2016 16:14:27 -0400
> Subject: [Equest-users] Boiler temperature for hybrid geothermal heat pump
> system
> Hi eQuesters,
>
>  I have a problem regarding hybrid geothermal heat pump system built in  a
> heating dominated building. From ASHRAE Handbook, it suggests that boiler
> be installed separately from geothermal heat exchanger loop due to high
> temperature of boiler.
>
> In addition, one report says that even if there are some cases that boiler
> has to be installed into GHX loop, the setpoint shall be 5-10F lower than
> GHX setpoint( e.g. 45F). That is because if the boiler is installed in the
> GHX loop, it is likely to dump heat back into the ground if boiler setpoint
> is higher than GHX setpoint.
>
>  However, heat exchange is related to both temperature and flow rate. With
> smaller size of boiler, can we allow to install boiler with higher setpoint
> higher than GHX setpoint into the GHX loop? Thanks!
>
> All the best,
> Siliang
>
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