Ground Source Heat Pump Monitoring (GSHP) Trewellard, Cornwall

The attached document provides details of the remote energy monitoring being employed to analyse ground source heat pump performance. It illustrates data from the web portal and a sample of degree day data from the energy analysis dashboard

GSHP Monitoring Cornwall

The following files illustrate

•  A sample chart from a web page report showing indoor and outdoor temperatures and the effect of heat pump operation on the evaporator entering and leaving temperatures.
• Information copied from an Excel file showing text data and a chart.

t-mac GSHP sample temperature chart

GSHP Text_chart

The third anniversary of monitoring this ongoing project passed at the end of May 2011 and the consultant, John Parker has presented the following report to the parties involved. John has used the logged data from remote GSM/GPRS equipment monitoring this installation to analyse the GSHP performance and he has kindly given his approval for it to be published as part of this project history.

John is Managing Director of Earth Engineering Ltd and one of the UK’s leading building services consultants specialising in the operation and development of ground source heat pumps.

He may be contacted at: jcwparker@compuserve.com

The 30th May saw the conclusion of the third year of my continuous monitoring of the HeatPlant35 system at Trewellard Road.

This is a 70m2 ground floor flat owned by the Penwith Housing Association on a site near Penzance and is occupied by a retired couple. It was retrofitted with improved insulation and a 3.5 kWth ground source heat pump during the winter of 2007/8.

Converted from an old radiator and coal fired back boiler system, heat from the heat pump is delivered by a new  low temperature 2 pipe  radiator system of sufficient  thermal mass to avoid the necessity of a buffer tank.

The original design calculations indicated a sp.ht. loss of 40W/m2 (at 21.0 / -1.0 oC)  leading to a Design Day heat loss of 2.86 kWth and an anticipated total annual thermal energy requirement of  8200 kWhth (split: 5600 htg. / 2600 hws). It was calculated that the system would be likely to run for 2400 hrs pa and would probably have an annual electricity requirement of 2350 kWhe.

The HeatPlant system is unique in having two quite separate control modes which improve overall thermal efficiency by permitting the radiators to operate at a lower temperature than the primaries serving the hws cylinder. It also allows the user to restrict the high temperature operating hours to that just sufficient to meet the daily hws demand.

There is no requirement for a supplementary heat source and the system is designed to store domestic hot water at 60oC.

It was hoped to achieve an annual SPF for heating and hot water of at least 3.25.

Commissioned in Spring 2008, monitoring started on 30th May and comprised of 23 separate parameters for which ‘snapshot’ values were recorded at half hour intervals and downloaded to a remote server which can be accessed (and analysed) on line whenever required.

After three years a total of 1,208,880 values are now logged into the database.

Annual reports have indicated the continually successful operation of the system (and the ongoing satisfaction of the tenants). This note is intended to provide a brief overall summary of the situation so far.  

In terms of service provided, specific tenant requirements have brought about a few small variations from the original design brief, as follows :

1.)    Space heating is enabled for all 365 days in the year and the internal temperature is maintained at 22-23oC at all times.[ This might be expected to increase the heating energy requirement by around 15% ]   

2.)    The tenants found domestic hot water at 60oC to be too hot and have selected the slightly reduced temperature of 53oC.They also prefer showers to baths and, since this is delivered by a direct acting electric shower unit, centralised domestic hot water usage is less than originally expected.[ These factors are likely to reduce system hws energy consumption, possibly by up to 40%]

After 3 years of operation the overall situation is as follows:

A total of 6720 kWhe has been consumed by the heat pump and ground loop pump, which have run for a total of 7917 hours.

4900m3 of water has passed around the load output circuit at an average operating temp.difference of 4.0 K.

This represents a total thermal output of 22850 kWhth and includes the supply of 65700 litres of domestic hws.

The overall SPF is  3.3

These basic facts can be expanded and presented as annual averages for greater clarity :

Electricity to run heat pump and ground loop pump = 2240 kWhe pa. at an annual run time = 2640 hours.

Normal operating F & R temperatures for space heating = 40 / 36 oC at a water flow rate =  0.172 l/s.

Maximum operating F & R temps for hws primaries = 58 / 54.5 oC at a flow rate = 0.178 l/s.

Total run time when delivering space heating = 1945 hours pa, and when charging the hws cylinder = 695 hours pa.

Delivered thermal energy into space heating system = 5600 kWhth, and into hws system = 1800 kWhth.

HP electricity use for space heating = 1650 kWhe pa.    HP electricity use for hws provision = 590 kWhe.

SPF for space heating = 3.39.        SPF for hws = 3.05.

Of the 1800 kWhth input to the hws system only 1000 kWhth (60 litres/day heated through 40K) was used to heat the water.

The remaining 800 kWhth, although considered losses from the hws system, are actually usefully used to supplement the total space heating need.

[The buildings total space heating useful energy requirement is therefore = 6400 kWhth if the useful hws energy is taken to be only 1000 kWhth.

Taking this view of the energy split would give a heating SPF = 3.9 and an hws SPF = 1.7]

Taking the present price of electricity to be 13.5 p/kWhe, the total annual cost for all space and water heating is  £302. 

[ Heat Balance Check : 

Monitoring the ground loop showed that  2639m3 of water/glycol mix is circulating annually at an average working DT of 2.0 K.

This amounts to 5732 kWhth of source thermal energy. Assuming casing and external pipework losses of 200 Wth this is equivalent to 530 kWhth pa, (or 7% of total output).

The source, load and heat pump systems can therefore be seen to be in energy balance.   Inputs: 5732 + 2240 = 7972.     Outputs: 5600 + 1800 + 530 = 7930 ]

Much more information and detail is available if desired and monitoring is continuing.

Best wishes,

John Parker.