@toodles 

Hi Toodles,

Nice to hear from a fellow Seventy-Six year old, OAP .

Water-Heating.

I  used my Heat Pump Water-Heater throughout the winter of 22-23 Only to be delivered of an Electricity bill more than 2 and a half times my Gas Bill for 2021.

This winter, 23-24,  I have stopped the Water-Heater but not the "Legionella Routine" with my Electricity consumption reducing by 10% .

With repayments of £42 per month , the Running costs of my Heat Pump became completely unaffordable!

Water-Heater or Space-Heater Priority?

 My Heat -pump also Switches between Water-Heating and Space heating based on a priority.

The Water Heater system works but................at a cost in kWh and £'s

I have thought of replacing the massive 200 Litre tank with a on-call Electric "under Sink" water heater, but , on seeing the costs thought better of it !

NIC

Installed by a company in Govan , Glasgow my heat pump has been a two year nightmare, with my "installer" being Struck-off Three times by the MCS/NIC for an assortment of failings, With the NIC finally admitting defeat , saying that " You (me!) are Not going to like this ........................

..............But Nothing can now  be Done , Good luck !"

I have finally come to the conclusion that Nobody is going to repair or replace my Heat pump .............

..........................and that the best that I do is simply admit that my system repair is "uneconomic".

I cannot afford to have this Heat Pump repaired or replaced, and , look with envy at the replacement Heat-pumps fitted by Heat-Geeks, see the Skill-builder You tube videos.

Your photograph looks a wee bit like me ...........

@iantelescope You mentioned; ‘

Your photograph looks a wee bit like me ...........

ian’

Commiserations Sir! 😉

Regards, Toodles.

Hi Toodles

I have been contemplating my Heat Pump Fiasco ............

Perhaps Hans Christian Anderson sums it up perfectly........

The King is in the altogether, but altogether, the altogether He's altogether as naked as the day that he was born The King is in the altogether, but altogether, the altogether It's altogether the very least the King has ever worn".

For naked kings read Heat Pumps!

Having been told, by the NIC, that, following the third STRIKE_OFF of my "Installer"

"You are NOT Going to like this ............but Nothing can be Done!"

Were it Not for the intervention of my Member of the Scottish Parliament, I would have faced a total bill of £14000 following the Striking OFF of my "installer" by the NIC.

The HES in Scotland initially refused to repay the Grant and loan because of the performance of my "installer".

In the event, a "Drawdown Payment " was arranged to provide me with the Grant of ~£5000 , while still having to pay £42 per month for the £2500 Loan!

I spent another £3500 on replacing the Microbore Pipes and the replacing ALL of the radiators.

I spent a further £922.80 when Told that "I Must remove my Gas boiler  .........it being "too difficult to install the necessary Valves etc".

ps. I look more than a wee bit like you Toodles!

@iantelescope As I said before regarding similarities of Fizoggs - Commiserations! Regards, Toodles.

The Control Philosophy for Heat Pumps

My Heat pump controls the Water Temperature by measuring the outdoor Temperature and using the Water -Law Graph :

The Y Coordinate of the Water Law Graph shows the required Water Temperature as the outdoor Temperature changes.

The Actual Water Temperature is found by adding an Offset Temperature using the Displayed Water -Law Thermostat:

With the required Water Temperature found by adding the Thermostat Offset to the  Water Law Graph.

Here, the 1.2 C Offset produces a Water Temperature of 42.4 C.

Required Water temperature = Water-Law-Graph( Outdoor Temperature) + Offset.

The Actual  Resulting Water Temperature is set by measuring the difference between the Required Water Temperature and the Resulting Water Temperature.

The Water Law Thermostat cannot maintain the Actual Water Temperature exactly at the Required Water Temperature , with the resulting water temperature  shown in the following graph:

The Water Temperature is here oscillating , or Cycling , with a period of ~10 Minutes.

When the Water Law Thermostat detects the Water Temperature falling below the  Required Temperature  a Power Demand is issued to the Heat Pump.

With Power heating the water , the Water Temperature sharply increases until stopped by the cycle Running Time.

The Water Temperature then fall exponentially with a time constant determined by the Volume ( Mass) of Water within the Water Pipes.

The Cycle is stopped when the Water Temperature again falls below the required Temperature.

If the Cycle time is Less than 15.. 20 minutes , and the Cycling is seen to run continuously the Heat Pump is considered to be "Short Cycling".*

A particularly violent example of "Short Cycling" on 15th / 16 th March 2024

Both the MCS and Samsung have issued Warnings about Short Cycling:

A MCS Warning

Notice here the emphasis on the Minimum Power that the Heat Pump inverter can supply, here, ~2.5 kw.

The Minimum Inverter power is every bit as important as the Maximum power!

Most manufacturers Do NOT publicise their Minimum Inverter Power, presumably because they have something to hide!

A Warning for Samsung users.

* See the DECC Reports on a 15/20 minute Lower limit for cycling time and an advised 6 minute lower limit for Running Time.

ian

p.s I hope I have not insulted you  by not "teaching your granny to suck eggs".

I Hope my Technical writing style does NOT offend!

Posted by: @iantelescope

↑

p.s I hope I have not insulted you  by not "teaching your granny to suck eggs".

I Hope my Technical writing style does NOT offend!

No and no.

Thanks for posting.

To Buffer Or Not To Buffer , that is the Question?

Spring 2024.....

With Spring my Heat Pump resumes "Short Cycling" as shown in the following graph:

What Causes Short Cycling?

With Heat Pump Power Controlled by an "Inverter" my Heat Pump reverts to Cycling below the Inverter Minimum Power, in my case ~2.5 kw.

Cycling Time is set by the time taken to Heat the volume of water in the water pipes in response to the Heat Pump inverter Minimum power.

Energy Equations at Inverter Minimum Power

The total Input Energy when operating at Minimum power is        

     Input_Energy = Minimum_Power X Run_Time .................................................................................................................................................................(1)

Where Run_Time is measured in seconds.

The Total Power consumed in heating the Volume of water contained in the buffer and the pipes        

  Energy Consumed = Specific_Heat_of_Water X Mass_of_Water_within Water_pipes  X Maximum_Allowable_Temperature _Drop_Across_Buffer .........(2)                

The Input_Energy must equal the Energy_Consumed , i.e. ................1 = 2

For my Heat Pump :

Minimum power = 2.5 Kw

Buffer Volume = 50 Litres.

Volume of Pipes = 6 Litres.

Maximum_Allowable_Drop_Across_Buffer = 5 C.

Therefore, for my Heat Pump:

 2.5 X Rum_Time  = 4.18 X 56 X 5

Therefore , the Run Time in minutes for My Heat Pump would be         Run_Time = 4.18 X 56 X 5 / (2.5 X 60)

giving a Run_time of ..............................7.8 minutes:

Trade Off between "Short Cycling " and Efficiency......

The Calculation above depends upon the Value of the "Minimum_Allowable_Temperature_Drop , here assumed to be 5C.

My Heat Pump Already has a Temperature Drop of ~5 +/- 2 C Across a Heat Exchanger.

With a further worst case Piping Temperature Drop of ~ 8 +/- 2 C the total Temperature Drop is Already ~14C .

At a these Water Temperatures , the Radiators are Already operating at an efficiency of X 0.63 When operating at the Specified Working Water Temperature.!

The Compromise !

Given that I cannot afford any further Temperature Drops across the Transmission network A Buffer was fitted in Parallel.

The Parallel Buffer Tank was originally installed to overcome the De-icing Problem.

The Parallel Buffer Tank has been successful in stopping the de-icing problem but NOT the "Short Cycling".

Given that the NIC says that "You are NOT Going to like this ...............but that , given  the application of extensive sanctions against your "installer" ,

NOTHING CAN BE DONE".

Hypothermia or Bankruptcy ?

ian

PS Please check my calculations against those given in the MCS Data Sheet .

pps Please forgive my "simplistic Technical authorship"

Installing  a "Serial" or "Parallel" Buffer to reduce "Short Cycling" ?

Following a visit from a French Samsung Engineer I had a friendly dispute about fitting a buffer in Series with the Input port of my Heat Exchanger

OR 

installing the buffer in Parallel , i.e. across the ports of my Heat Exchanger.

The Frenchman was amused by my description of the "in Series" or "in Parallel" electrical speak!

The Parallel Buffer Across the Heat Exchanger Ports 

My Heat has , currently, a buffer fitted between the ports of my Heat Exchanger.

When operating above the Minimum Inverter power of ~2.5 Kw the Heat Pump Power is controlled by the Inverter.

When operating below the Minimum Inverter power , the Heat Pump reverts to Cycling power control.

When cycling, the Power from the Heat pump is used to heat a volume of Water , here, when operating "in Parallel", equalling the Buffer Volume plus the volume of the Heat Exchanger.

The Heat Exchanger volume is unknown but is thought to be insignificant compared to that of the Buffer Tank.

When operating at Minimum Power the Energy input to heating the Water in the Buffer Tank is:

Input Energy Required to heat Buffer tank = Minimum_power X Run_Time ( Seconds) ...........................................(1)

The Input Energy is used to heat the Buffer tank:

Energy consumed in heating water  = Specific_Heat_of_Water X Buffer_tank_Volume X Temperature_Difference _Across_Heat_Exchanger_ports...........(2)

where the Temperature_Difference _Across_Heat_Exchanger_ports is found by a pair of 18B20 Sensors, found to be ~4 C.

On equating 1) and 2) :

2.5 X Run_Time  = 4.18 X 50 X 4

Therefore:

Run_Time ( Minutes) = 4.18 X 50 X 4/(2.5 X 60) = 5.57 Minutes.

The Actual Run_Time measured is shown in the Graph:

With a Measured Average Run_Time of 5.16 Minutes.

The Run_time Calculated for the case of the "in Series" Buffer Tank was 7.8 minutes.

Conclusions

The fitting of a buffer Across the ports of my Heat Exchanger make little difference to that of fitting the Buffer "in Series" with One of my  Heat Exchanger ports!

When the buffer tank is fitted Across the Heat Exchanger ports ,"Short Cycling" is  a function of the Heat Pump Minimum Inverter Power , the Temperature Drop Across the Heat Exchanger Ports and the Buffer Tank Volume.

In Parallel , the Buffer acts as a shorting load across the Heat Exchanger ports, although, I have not, as yet,  measured the resulting losses.

In parallel , the losses are shown on the following graph:

With an average loss of  24.8 % including the Heat Exchanger , Parallel Buffer and piping.

When the buffer tank is fitted in line with only one Heat Exchanger Port , i.e. "In series operation ","Short Cycling" is  a function of the Heat Pump Minimum Inverter Power , the Temperature Drop Across the Buffer tank  and the Buffer Tank Volume.

When the buffer tank is fitted in line with only one Heat Exchanger Port , i.e. "In series operation", the Operating Water Temperature as displayed on the Heat Pump front panel , will be  significantly reduced . The Radiators will emit significantly reduced power.

@Mars

The Costs of "Short Cycling".

My Heat Pump is "Short Cycling" as shown in the graph

This "Short Cycling " results in motor wear & water contamination :

Water contamination is covered by the BS7593 Directive : Issued in 2019 to replace Similar EEC Directives.

The Following is an edited version of the BS7593 :2019 instructions provided by Fernox .

ian