Are air source heat pumps noisy?

The simple answer is NO but what is noisy? Modern air source heat pumps are significantly quieter than units produced say 5 years ago. This is primarily due to advances in the development of fan technology and improved chassis design which reduces vibration. 99% of sound generated by an air source heat pump is the movement of air. The sound levels will vary depending on the ambient temperature. The colder it is outside the faster the fan spins and vice versa. In the middle of summer the fan may not even spin.

For the purposes of the MCS Planning Standards for air source heat pumps the back ground noise is assumed to be 40 dBa or lower. For compliance with planning regulations and permitted development rights the air source heat pump must be 42 dBa or lower from the assessment position.  The assessment position is the distance between the unit and a neighbouring property.

The positioning of the unit is critical to meeting the maximum sound levels. Obstacles such as walls and fences can increase the noise levels over the design conditions. A well designed air source heat pump system must allow for the displacement of the air. This not only reduces noise but also increases the efficiency of the heat pump.

When the noise exceeds the maximum permitted levels the unit can be installed in an acoustic enclosure or sitted far enough from the assessment position to meet the regulations. Heat pumps can be located up to 30m from the property before other design considerations are imposed.

To reduce sound levels  manufactures are encouraged to meet the standards set out by the Noise Abatement Society and  awarded the Quiet Note if the heat pump is within the standards. The Mitsubishi Ecodan was the first heat pump to be awarded the Quiet Note in the UK.

DeLonghi Air source heat pump - high temperature - acoustic louver enclosure

Specification of Commercial Ground & Air source heat pumps

The unique thermal characteristics and demands of a commercial building often means a traditional approach of separate boiler and chiller is taken to meet the peak heating and cooling loads. Due to increasing operational and energy costs, renewable technologies are becoming more common in modern developments but very rarely used to their full capability. There is a growing demand to increase sustainable value to a development and utilise natural resources more efficiently. Ground and air source heat pumps can replace or integrate with new and existing applications to provide; heating, hot water and cooling, efficiently as possible while reducing carbon emissions.

Although heat pumps in general offer the highest return on investment and lower energy bills, the initial capital cost can discourage developers and end users from investing in the technology. This is not to say heat pumps are the only solution. A majority of commercial heating and cooling applications operate at part load conditions throughout the year. The integration of a heat pump with gas\lpg or oil boilers can significantly reduce investment and operational costs while still meeting the design conditions.

Research carried out by construction consultants Sweett Group and BRE found that office developers typically invest up to 2% more when targeting higher BREEAM ratings, and recover that additional investment in two to five years through savings in their energy and water bills. The same research found that achieving lower BREEAM ratings can incur little or no additional cost.

There is a greater opportunity to specify recovery heat pumps which recover rejected energy from the cooling cycle to provide simultaneous heating and cooling with huge energy savings. This can be improved even further with a recovery ground source heat pump as rejected energy can be stored in the borehole array and harvested during the heating operation increasing the COP.

We offer a turnkey solution for all types of commercial heat pump systems from 5kW to 1MW.

We supply equipment as approved installation and service partners for; Dimplex, Thermia, Danfoss, Carrier, Clivet, CIAT and Climaveneta.

South West Energy Services – Thermia 42kW Ground Source Heat Pump

New Build - Thermia - Ground Source Heat Pump - Vertical bore holes - heating - hotwater - swimming poolThis exclusive new build development in Cornwall has been built with no expense spared. To meet the standards required for an A rated energy efficient house a Thermia ECO 42kW ground source heat pump with 8 x 100m vertical boreholes distributed from a sealed manifold chamber. The heat pump supplies a 500L heating buffer tank and 2 x 250L heat pump optimised hot water cylinders. The buffer tank supplies the wet under floor heating system and indoor swimming pool.

The ground collector is flushed and filled with a diluted Ethylene Glycol mixture (20%). THERMOX DTX has been tested and classified as Non-Toxic 1 by an EPA 2 certified Laboratory.

The heat pump is capable of storing domestic hot water at 60˚C with a secondary return that pumps the hot water around the building meaning you have instant hot water at tap outlets.

To increase system efficiency and performance, the Thermia Solution Controller has been specified. The web based user interface allows remote monitoring of the system with;

  • Access to control strategies and interface parameters
  • System overview
  • Datalogging with presentation in graphical charts
  • Alarm notification through e-mail or SMS

Due to the varying load conditions during the `bedding in` period (12 months), South West Energy Services Ltd, provide a FREE service where we will monitor and optimise the system remotely.

As this is a self build the client will be entitled to the Domestic RHI which will generate a revenue of £40,000 over the next 7 years.

South West Energy Services - Cornwall - Thermia ECO 42 Ground Source Heat Pump - 500L Buffer Tank - 2 x 250L DHW Cylinders - 8 x 100m boreholes - - Domestic RHI

The importance of borehole design for ground source heat pumps

Here is some guidance on the importance of a professionally designed and installed borehole for a ground source heat pump. I have included some technical guidance from the Ground Source Heat Pump Association and MCS GSHP Design Document, regarding the sitting and installation of bore holes. This will hopefully provide you with a better understanding of the correct process for drilling and grouting. Unfortunately a majority of companies do not use a thermal grout, partly due to keeping costs down but also a complete lack of understanding to what is happening in the ground. The water table alone will not suffice.

Borehole spacing and sitting is critical to optimising the extracted energy from the ground and sun. Where boreholes are positioned in close proximity to fixed structures (>7m) the impact of reduced ground surface area on the recovery rate from solar irradiation must be considered.(there is very little geothermal energy extracted, 99% is from the sun). The efficiency and composition of a borehole and probe is calculated using the following criteria;

Abstraction rate for the type of ground\geological make-up.

  • Borehole depth
  • Borehole spacing (distance between boreholes or structures)
  • Solar irradiation
  • Borehole probe construction (32mm or 40mm HPDE)
  • Type of thermal grout

Yes there is the option of energy piles but would you really use this on a domestic project?

We have been designing and installing ground source heat pump systems for over 15 years and built a reputation nationally as a market leader and pioneer in the industry for both domestic and commercial projects. We provide consultancy, design services and training, not only to our competition but also to heat pump manufactures\suppliers. We are one of only a handful of contracting companies in the UK, who provide CPD training to Architects on ground & air source heat pump design.

We are happy to loose a project to a well designed and installed system, unfortunately there are very few out there which is why we try and provide as much guidance and knowledge as possible even if not our job. Anyone can install a heat pump its no different to a boiler. It comes down to design, best practice and experience. The most important part of a GSHP is the ground array as it provides 75% of your energy demands and it’s the one part you can not see once installed.

If you have any questions regarding the drilling process please speak to our drilling partner ADP to see how one of the largest drilling companies in the UK operates.  Tom Page is the MD and can provide you with impartial advice on how a bore hole should be designed and installed. Dont mention you are speaking with South West Energy Services, and see what he has to say.

2.8 Party Wall Issues 

All systems shall be designed assuming that adjacent systems will be installed and will therefore have a right to the heat under their property.


8.1 General 

Grout thermal conductivity is an important aspect of ground heat exchanger design. The designer shall be responsible for selection of the grout to support the foundation of the ground heat exchanger design. The following standards relate to the materials and methods of testing and verification of properties, as supplied by the manufacturers.

8.2 Grout Thermal Conductivity

Grout material thermal conductivity shall be determined by the following tests or comparable to EU standards:

  • Pliable materials – American Society for Testing and Materials (ASTM) D-5334 “Standard test method for determination of thermal conductivity of soils and soft rocks by thermal needle probe procedure”
  • Rigid materials – ASTM C-177 “Standard test method for steady heat flux measurements and thermal transmission properties by means of the guarded hot plate apparatus”

Materials that are bentonite-based are classified as pliable materials and cement based products or grout mixtures containing cement that cause the product to become rigid once cured are classified as rigid materials.

9.4 Ground Heat Exchanger Installation

The borehole shall be grouted from bottom to top with a suitable recognised geothermal grouting material and tremmie pipe as outlined in section 8.


3) MIS 3005 requires that the design of a GSHP system will lead to a minimum entering water temperature (EWT) into the heat pump from the ground of 0°C over the lifetime of the installation. Assuming a possible temperature difference of 3°C, an average minimum ground loop fluid temperature of -1.5°C has been adopted here.

This temperature defines some of the properties of the antifreeze solutions.

A) Heat pump thermal output. This is can be taken as the manufacturer’s MCS approved quoted output at B0/W35.

I know this is a bit War and Peace but I am a big believer in pass on the knowledge, it’s the only way the industry will improve and grow.

Please look at our case studies page for the types of projects we are involved in.


Are Solar Thermal Systems a good idea?

One of the most common questions we are asked; Is solar thermal a good addition to a ground or air source heat pump system?

The simple answer in most cases is NO. Hot water accounts for 20% of the annual domestic fuel bill. Solar thermal will cover on average 70% of your annual hot water consumption, so really doesn’t provide very much unless you have a very high hot water demand. The RHI pays back around 80% of the installation cost paid back over 7 years. Financially it doesn’t stack up. Plus you have the annual service cost which would be higher than what you would save. With modern high efficiency buildings, solar thermal can be integrated in to a low temperature heating system and cover around 20% of the annual heating load. Unfortunately the RHI does not provide payments to Solar thermal systems & space heating.

In our opinion you are better off in investing in a Solar PV system even though the tariff has been recently been cut. A 4kW PV system can reduce the heat pumps predicted running costs by around 20% plus generate a revenue for 20 years with the FIT. PV still makes sense if you have a heat pump. It would also provide more free hot water than a solar thermal system. Why pay for 2 installations when 1 does it all!

At South West Energy Services we highly recommend Solar thermal systems for indoor and outdoor swimming pools and where there is a higher than average hot water demand (changing rooms or communal showers).

Solar thermal system - evacuated tubes or panels with air and ground source heat pumps