FAQ's

Heat recovery ventilation and underfloor heating

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How does a heat Pump Work?

The Physicist, Robert Boyle is attributed with publishing the original gas law in 1662, a liquid refrigerant with a low boiling point absorbs through a evaporator the source energy provided by the air or through the ground via collectors or boreholes, the higher the source energy the more efficient the heat pump will be (COP). The refrigerant containing the free energy is drawn by an electric scroll compressor which further increases the pressure which turns the refrigerant from a liquid into a gaseous state; this energy is extracted via another heat exchanger (condenser) to produce the energy for your heating requirements. The refrigerant continues on its way via the expansion valve and returns back to a liquid for the process to continue.

 

What are the best rated heat pumps?

The energy efficiency for heat pumps (ground & air source) is rated by the term C.O.P (Coefficient of Performance/Potential):

 

An important issue regarding efficiency (C.O.P) is how big a role the outside source temperature plays. When it comes to ground source heat pumps, the temperatures in the winter time remain relatively high (8 - 10°C) which greatly improves C.O.P but it comes at the additional cost of groundworks/boreholes etc. Ground Source is the best solution from an energy effectiveness perspective and we would always recommend ground source as your best option for that reason.

 

What does 'COP' stand for?

The efficiency of a heat pump is given by its co-efficient of performance (COP), which means the thermal output divided by the electricity consumed.

 

What size heat pump would I need to heat my property?

It is essential that buildings are designed for energy efficiency from the outset; thermal losses need to be kept to a minimum as this has a direct relationship to the amount of energy required – thermal insulation and intelligent ventilation are important. It is not always the most energy efficient and cost effective way to design a heat pump system to supply the total design load, we live in a temperate climate and experience little very cold weather.

 

How can i achieve a higher 'COP'?

High COPs are achieved if higher temperatures are available through the ground loops, temperatures vary from 5 to 12°C, and poor design of the ground loop system may have an adverse effect on the recovery temperatures.

 

Can I increase the efficiency of my heat pump?

Air tightness requirements for buildings means that Heat pump systems can take full advantage of heat recovery and ventilation, HRV units extract the warm air through a heat exchanger to pre-heat outside air reducing the heating load. The lower the UFH system is designed to operate at, will increase the energy efficiency and lower your running costs, we would also recommend the use of weather compensation.

 

Are heat pumps really energy efficient?

Good control is paramount to your system’s energy efficiency and it comes in many guises; weather compensation, system monitoring, variable speed pumps, buffer vessels or individual room controls - how these are integrated and monitored into your system play a vital role in your energy efficiency.

 

What is an exhaust air heat pump?

These are designed for small dwellings and extract air via duct work connected to the warm areas of the building such as bathrooms, kitchens and utility rooms. The air is taken from the warmer areas of the building and transferred onto the heat pump's refrigerated circuit, which allows it to heat either water or the building it's self, recently they have been recieving a lot of bad press due to innappropriate use and poor design.

 

Can I use radiators with a heat pump?

In thoeory Yes, but we would try to avoid it if at all possible, we would recommend using low water content fan convectors, traditional radiators are designed with a delta T of 50 degrees, basically to achieve a air temperature of 20 a water temperature of 70 is required, therefore that is why as a 'rough rule of thumb' they need to be double the size.

 

What does the term 'future proofing' actually mean?

Subheat believe in 'future proofing' your energy system now; so if you are currently considering a low energy heat source (heat pump), we believe it is vital that the underfloor heating system is designed correctly so that it gives you the option to seamlessly move to a renewable energy source in the future.

 

What is a buffer vessel?

The aim of a buffer vessel is to remove the possibility of any short cycling of the heating appliance; it acts as a system separator for extending the heat pump operating time and for partially bridging power OFF periods as well as the hydraulic separation of the flow from the heat pump and the heating circuit. Correct sizing is vital with particular regard to Air source and its defrost cycle.

 

What are the advantages of a buffer vessel?

A buffer vessel can also be used for multiple take-offs for additional heat sources such as solar and fossil fuel boilers and a buffer vessel is generally required for the defrost cycle of Air Water heat pumps, a buffer vessel also allows for complete zone control of the heating circuits. It also plays a part in the efficiency of your heat pump alloowing for longer run times. Particular importance must be made to the correct sizing of the heat exchanger/s

 

Can I have zone control without a buffer vessel?

You can install heat pumps without buffer vessels but a constant heat pump flow rate is required so you would need at 20 to 25% of your heating circuits to be open and not be controlled by individual thermostatic actuators to allow flow from the heat pump and prevent short-cycling occurring, inverter heat pumps would be preferable.

 

Can I install a heat pump without a buffer vessel?

Failure for not allowing the nominal flow rate may result in the heat pump experiencing a high pressure shut down. A buffer vessel may not be necessary if the heating circuits have no requirements for zone control such as large area heating systems, but again good design of the heating system is of paramount importance.

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