This trial demonstrates how the addition of ebm-papst’s new AxiTop diffuser to existing EC HyBlade axial fans can provide significant energy savings from 15 per cent to 51 per cent on condenser packs running at part load and even improvements of 26 per cent at full load. The conclusion observes that upgrading existing systems with AxiTop can not only improve the efficiency of the fans but also improve the efficiency of the whole system.
What is AxiTop? 
The AxiTop diffuser has been developed to fit the ebm-papst range of HyBlade axial fans as supplied to all the major refrigeration plant manufacturers. It is also ideal for retrofitting existing fans by providing a simple solution to upgrade those installed across the estate. An upgrade that reduces the noise, decreases the power consumption and increases the fan performance.
A scale of possible energy savings – or efficiency enhancement and noise reduction – can be achieved with an optimal diffuser. By simply replacing a standard fan with a guard grille for one with a support arm, guard grille and AxiTop diffuser, savings of up to 27 per cent can be achieved in terms of power consumption, while operating noise is reduced by up to 7.2dB(A).
Operated at the same operating point, energy savings of up to 27 per cent and 7.2 dB(A) less noise development are possible, depending on the application. (measured on size 800 mm)
Condenser trial
An AxiTop trial was conducted by Space Engineering Services and Coolers and Condensers on behalf of a major UK supermarket with the aim to evaluate the energy saving benefits of retrofitting existing EC condenser fans with the new AxiTop diffuser.
Sub metering and temperature logging were applied to four Condensers, two identical Low Temperature (LT) packs and two identical High Temperature (HT) packs, and recorded for four weeks.
The AxiTop product was fitted to two condensers, LT2 (three fans) and HT2 (five fans). The other two packs were used as a base line for comparison.
Sub metering and temperature logging continued for a further four weeks.
HT pack data results
Graphs 1 and 2 show the before and after data for the HT packs. The data is recorded on the same trading day (Saturday) with almost identical average ambient temperature conditions.
The Red trace is the base line unit HT1 which shows a total power consumption of 9.31kWh before and 9.1kWh after which are almost identical readings taking into account the different tolerances on different days.
The Blue trace is from the converted unit HT2 which shows a reduction in total power consumption from 13.04kWh to 11.09kWh which is a 15 per cent reduction due to AxiTop being fitted.
**Graph 1: Before Data – Ave Daily Temp 13.7°C
**Graph 2: After Data – Ave Daily Temp 13.8°C
LT pack data results
Graph 3 and 4 show the before and after data for the LT packs. The data is recorded on the same trading day (Saturday) with almost identical average ambient temperature conditions.
The Red trace is the base line unit LT1 which shows a total power consumption of 4.14kWh before and 4.2kWh after which are almost identical readings taking into account the different tolerances on different days.
The Blue trace is from the converted unit LT2 which shows a reduction in total power consumption from 18.23kWh to 8.9kWh which is a 51 per cent reduction due to AxiTop being fitted.
**Graph 3: Before Data – Ave Daily Temp 13.7°C
**Graph 4: After Data – Ave Daily Temp 13.8°C
HT pack data results on the hottest day
Graph 5 and 6 show data from a two hour window on the hottest day before the retrofit compared to a similar day after conversion. The data is recorded on the same time period, on the same trading day (Monday) with near average ambient temperature conditions.
The Red trace is the base line unit HT1 which shows a total power consumption of 18.5kWh before and 17.5kWh after which is a drop of 1kWh (0.5 per cent).
The Blue trace is from the converted unit HT2 which shows a reduction in total power consumption from 18.5kWh to 13.6kWh which is a 4.9kWh or 26 per cent reduction in this two hour period due to the AxiTop being fitted.
**Graph 5: Before Data – Ave Temp 20.7°C
**Graph 6: After Data – Ave Temp 19.5°C
Discussion
Based on identical trading days with the same ambient conditions, it was shown that the base line packs HT1 and LT1 have performed almost identically.
The AxiTop packs HT2 and LT2 however showed significant savings of 15 per cent and 51 per cent respectively.
It is clear that the LT2 pack improved significantly more than expected and this is believed to be due to the siting of LT2 which is partially surrounded.
Other than improving the efficiency of the EC axial fans by converting dynamic pressure into useful static pressure, the AxiTop improves the throw of the fan and can prevent air recirculating within the unit when siting conditions are not ideal. Diagram 1 shows a simulation of how the diffuser straightens and improves the throw of the Axial fan.
Diagram 1:
During high ambient conditions Graph 5 shows identical power consumption for both HT condensers with all fans running at their maximum. Following the conversion of HT2 there is a marked reduction due to the AxiTop diffuser of 26 per cent even with the fans running at maximum speed.
With diffuser
Without diffuser
When the trace drops as shown in Graph 6, this shows the discharge pressure set point from the pack is being achieved and so allows the fans to ramp down. HT2 is achieving this more often than HT1 and for a greater length of time so energy is being saved not only from the fan energy reduction but also from the compressors as well.
Current and Potential Future Applications
The Axitop Diffuser is used on sites with condensers, coolers and chillers. Future applications could involve the upgrade of sites where noise levels are an issue. The product also offers the possibility to boost the air performance of fans on equipment that has been incorrectly sized for an application. The added benefit of the AxiTop is the reduction of energy usage as demonstrated through the above trial.