Open loop or Closed loop???

dcom

Hi,

I am trying to decide between open vs closed loop system.

The open loop system I am considering draws water from your domestic well, the heat is extracted from this water then the water is is sent backdown a second well.

On paper, the open loop system (water to water) seems to be the more efficient, cheper etc

One of the only negatives for the open loop is the water pump maintenance. We have to maintain the pump anyway as we are using the same one for our domestic water

Our well has a flow rate of 3 litres per second which is good enough to feed the heat pump.

Anybody got any views on open vs closed loop systems?

Longboard

Open loops are generally cheaper to install as you do not have to drill to the same depts as a closed loop. However you do have an additional pump in the system when compaired to a close loop (unless heaven forbid you run the well water through the evaporator plate) This adds to the running cost. There is also maintenance required to empty the stainer in order to keep flow rates up.

I presume a pump test was carried out to obtain a figure of 3 litres a sec?

Close loops are more expencive due to the extra driling dept required to accomodate the cooling load. However they need next to no maintenance provided sufficent anti freeze is installed and there are no leaks. If there is any leaks you will have to top up the system periodically. Usually domestic water pumps and closed loops cannot be installed in the same well.

What size system is going into the house (kW)? What is the COP of the system?

I would generally go for the closed loop. It is more expencive but usually less hassel as it eliminates unknowns/maintenance associated with open loops.

dcom

Thanks Longboard.

The figure of 3 litres a sec was given by the company who sank the well, not sure how the measured it, as I wasnt onsite

The supplier of the open loop system has told me that before we can decide the water has to be independantly tested, as high manganese can harm the open loop system.

Its a 14kw hautec pump, not sure what the COP is for this pump as the only information I have at the minute is in German cant find the technical specs in English online will request a hard copy from the supplier.

I was reading about open loop vs closed loop in general and the stuff I read said open had a higher COP.

You said 'Usually domestic water pumps and closed loops cannot be installed in the same well.' so its ok for an open looped system to be installed in a domestic water well??

Longboard

A pump test is usually carried out over 24hours to see if the water table can sustain the flow rate over that period without dramatically affecting the height of the water table.

Manganese (black gunk) can clog plates, valves or strainers quickly. Your supplier sounds like they know what their doing.

The majority of heat pumps have an average a COP of 4.0 for 0'C/35'C. Going by that a closed loop for a 14kw system with a 10.5 KW cooling load will probably need a total collector dept in the region of 200m.

The open loop is the better performer provided the system does not deterorate ( regular maintenance of strainer & plate)

I know that you cannot fit the domestic pump in the closed well because of space restictions with the single/double loop probe. There is also the issue of grouting the well and the fact that the closed loop contains antifreeze that may leak (rare and in small amounts, At the least Propalene glycol (food grade) should be used).

I cannot say for definate either way with regards to the open loop well.

The above is not gospel.

holdfast

I guess flow rate is ok if you can sustain it, can remeber where this was done in cork city but flow rates were way higher it was a aquifer under pressure

Water quaility is very important. I would think extra cost of running water pump plus heat pump may not be ideal. It would reduce you cop.

Without doing any figures go for closed loop in different holes, also reduces chance of your well getting polluted(what will you do with the water if you dont use it run it back down the well again) as this water would not be ideal for consumpation after running passed through heat pump ????

Sorry not an expert but I have enough knowledge to be dangerous

Longboard

The well water should not come into contact with material (systems usually contain non corrosive stainless steel / bronze / MDPE or HDPE etc) that would "contaminate" it. The installer can confirm this. The only property altered would be the temperature which would be a few degrees cooler for heating systems.

The pump would consume about 3.5kW of electricty (mostly running the compressor and 2 circ pumps). Adding an open loop pump would increase this figure by about 0.2kW (conservative). Any increase in consumption would be offset by the improved recovery rate of the heat sink (well water). Most commercial installations go with open loop where source allows because of the savings made by using a more efficent collector.