Super efficient ground-air heat exchanger
September 26, 2008 by admin
Filed under Renewables
What is described as a “super efficient” ground-air heat exchanger system has been launched by ADM Systems. It claims a Coefficient of Performance (COP) of around 50. This compares to a COP on ground-source heat pumps of around 3-4. It significantly reduces the amount of energy the mechanical ventilation with heat recovery unit (MVHR) system requires to heat or cool the incoming air.
It does this by exploiting the natural temperature of the ground to provide a cost effective source of renewable energy. At a depth of 1.5 to 2m, the earth’s temperature is a constant 8-12˚C throughout the year.
By drawing air through an underground network of pipes, it is either pre-heated by the ground in winter or pre-cooled in summer. In combination with an ADM Systems MVHR unit this significantly reduces the heating and cooling costs of a building.
For example, an outside air temperature of -5˚C during winter can be raised to +4˚C by the heat exchanger, before it enters the MVHR unit, based on a constant average ground temperature of 10˚C. Similarly, during summer a 28˚C outside air temperature can be pre-cooled to +16˚C, again by using the heat exchanger and constant 10˚C ground temperature, before it enters the MVHR unit.
Chris Marriott, ADM Systems’ managing director, says: “We’ve had a tremendous response to the new system from customers looking to significantly reduce their heating and cooling costs in the building. By using the earth’s natural stored energy we are able to offer an amazing COP of around 50.”
The MVHR units, fitted with the new system, works by a series of ducts that collect stale moist air from inside the house, from areas such as the kitchen, laundry and bathrooms. This stale contaminated air passes through the MVHR unit and is exhausted to the outside. Clean fresh heated (or cooled) air from the heat exchanger is then drawn into the MVHR unit, as the two air streams pass each other, the heat is transferred from the outgoing stale air to the fresh incoming air.
There is no mixing of air streams. During winter, the system is able to capture over 90% of the energy from the outgoing stale air before delivering it as warm filtered, preconditioned air into the living areas of the property through the ducting.
ADM Systems is able to offer customers bespoke design software to calculate the expected output of the system, based on UK weather data. This software shows the kilowatt-hours per annum that can be saved in both heating and cooling operations and also the COP of each project.
More information: www.admsystems.co.uk
To claim a COP of 50 COMPARED to a GSHP of 3-4 is completely wrong, sorry to say. To compare with the GSHP, the MVHR must also be included in the numbers, not only the coil, otherwise we are comparing apples and oranges.
The COP should be defined as the work required to supply the energy needed for heating. Another thing the manufacturer doesn’ät include is the fact that GSHP’s often produce also DHW, which is not the case here.
A better analysis of the COP would therefore be welcome.
Cheers, Roger
Thank you Roger, I have passed this onto the Ed…. will he dare to wade in ?
Thanks for your comments Roger. I know this is a bit of a cop-out but, obviously, we are only as good as the information we are sent. So we are indepted to people such as yourself for drawing our attention to any shortcomings. I will bring this to the attention of our source of this information and see what comment is forthcoming. Watch this space.
Regards
Andrew
(Editor 4PROecotips)
Comment from ADMSystems
The COP stated here is related to the fan input energy needed compared to the energy generated by the heat transfer. You are correct it does not take into account the MVHR unit, the reason being that in some cases a simple inline DC fan is used for drawing the air in, which in this case, the COPs stated are achievable. We do not attempt to compare directly the GAHE to a GSHP as one is for ventilation (but provides pre-heating and pre-cooling) and the other is for space heating. The aim of the statement is to show that very little energy is actually needed to run a GAHE itself, hence why it is an energy-efficent system. REHAU, the manufacturer, have design software which was developed in conjunction with the Passivhaus Institute in Germany for calculating estimated energy savings for each project.