For your heat pump system, is a thermal buffer tank necessary?

A buffer vessel, sometimes referred to as a buffer tank or thermal storage tank, is an element that enhances the performance and efficiency of most air source heat pump (ASHP) systems.

In essence, the buffer vessel is a thermal reservoir comprised of a tank filled with water. Decoupling the heat pump from the cooling or heating distribution system is its main purpose, and it offers the following advantages:

Enhancing Heat Pump Performance:

By enabling the heat pump to run at maximum efficiency for longer periods of time, buffer tanks can raise the system’s overall efficiency. System performance may improve, and energy savings may arise from this.

Reducing Cycling:

The heat pump’s on/off cycling is lessened using buffer vessels. Continuous operation at a constant load is the most efficient operation for air source heat pumps. The need for heating or cooling in a structure can, however, differ. The buffer tank keeps the heat pump from starting and stopping frequently, which can result in poorer efficiency, and enables it to run at a constant output for longer periods of time.

Improving System Stability:

The heating or cooling system is more stable when buffer vessels are used. When demand is low, they retain the heat pump’s extra energy and release it when demand is high. This contributes to a more constant and cosy interior temperature.

Enhancing System Control:

By providing a volume of water that can function as a thermal mass, buffer tanks help to slow down the rate at which the water’s temperature changes. This may facilitate more accurate control over the heat pump’s performance and better temperature fluctuation management by simplifying the system’s overall control.

Reducing Wear and Tear:

The heat pump’s components may experience wear and tear because of frequent cycling. By lowering the quantity of on/off cycles, the buffer tank helps to prolong the heat pump’s lifespan and lower maintenance needs.

Three key points for the use of buffer tanks in heat pump systems

Increasing the amount of water in the heating system is the aim. By preventing short cycling, buffer tanks balance the system and ensure that the heat pump operates well. In the absence of a buffer tank, the heat pump constantly modifies its operation by turning on and off, which increases wear and tear, particularly in unpredictable spring and autumn weather.
A heat pump system’s two circuits can operate simultaneously as independent and cooperative units thanks to buffer tanks.Why is that relevant? To function optimally, the two circuits require distinct flow rates and temperatures. The circuit for “giving out heat” (such as radiators or underfloor heating) shouldn’t use the same logic as the heat pump circuit.
By supplying heat from the buffer tank to aid in the defrosting process without drawing heat from the house’s radiators, the buffer tank helps the heat pump defrost cycle.

Additional benefits

The heat pump compressor is successfully shielded by buffer tanks against excessive strain and expensive failure.

Similarly, in the absence of a buffer tank, a heat pump system will need to provide extra heat through radiators and/or underfloor heating.

In addition, homeowners who do not have a buffer tank lose out on the opportunity to zone their heating, fully regulate the heating system, and switch off the heat in specific rooms. In the long run, a system without a buffer tank may be less expensive overall, but it will also be less comfortable and possibly overheated.

Conclusion

Not every air source heat pump system will need a buffer vessel. The particulars of the building, the anticipated fluctuations in demand, and the heating or cooling system’s design all influence whether a buffer tank is necessary. It can be determined whether a buffer vessel is required for a certain ASHP installation by speaking with a heating system expert, however, they generally benefit a heat pump and the HVAC system.

For our full range of buffer tanks from Flexiheat UK, please see the following webpage: Buffer tanks

2000 Litre buffer tank or vessel

What is a buffer tank?

First, we must clarify what a buffer tank does, as they are ideal for use in renewable and traditional heating systems, including gas, biomass, or oil boilers, as well as solar thermal and heat pumps (both air source and ground source heat pumps).

Definition and purpose of buffer tanks

A buffer tank retains thermal energy via thermal storage for later use and can supplement the heat source when demand is high or store heat (heat sink) when demand is lower. Stored energy in the form of heat can be immediately accessed without the heat source needing to get up to temperature, which is useful for maintaining a constant output over time for your heating hot water systems.

The benefits of using buffer tanks in heating and cooling systems

Buffer tanks provide a reliable and efficient heating solution because they store heat for later use by the heating system. They can decrease the number of on/off cycles of the heat pump due to stored heat in the buffer tank or vessel.

For chilled water thermal storage systems, which are often used in air conditioning systems to improve thermal inertia, the buffer tank is insulated in such a way as to keep the temperature as low as possible.

All of our buffer tank ranges have high thermal insulation levels and comply with the ErP insulation requirements, which cover buffer tanks up to and including buffer vessels or tanks up to 2,000 litres in volume.

Conformity to standards

All of these buffer tanks comply with both Article 4 , Paragraph 3 of the Pressure Equipment Directive (PED) 2014/68/UE and the ErP Directive EU 812/2013 for energy-related products.

Buffer tank options for 2,000 liters of heated or chilled water

We have two main options: hot water storage (2000 litres) or chilled water storage (2000 litres).

Option 1

Our “PSS Buffer Tank Range” has two standard options: one buffer tank that is suitable for both heating and chilled water systems, and one buffer tank that is only suitable for chilled water systems.

Both options have six x 4″ female BSP tappings and 3 x 1/2″ female temperature probe or gauge ports on the buffer tank.

With a maximum working pressure of 6 Bar and maximum temperature of 95°C for both buffer tank options.

A diagram showing the connections of our 2000L buffer vessel for heating and chilled water with a maximum working pressure of 6 bar and 95C temperature from Flexiheat UK

2000L Heating or Chilled water buffer tank -PSS range with 6 connections

The heating and chilled water version has 80mm polyester with 20mm PEXL insulation. This is a polyethylene foam that stops water vapour diffusion, protecting the buffer tank exterior from dew and corrosion. Because of its extremely low water absorption, the lagging effectively doesn’t absorb any water. This results in a class “C” ErP insulation level for the material.

Technical data showing the connections on our 2000 litre buffer vessel or tank for heating or chilled water from Flexiheat UK

Both the 1,500 Litre and 2000 Litre buffer tanks – have the same connection sizes.6 Bar working pressure (unlike many of our competition which only offer 3 Bar working pressure)

Since chilled water units do not fall under the ErP regulations, the chilled water buffer tank option only has 25-mm PEXL insulation.

Download the PPS Buffer tanks for heating and chilled water – 25 litres to 2,000 litres capacity brochure from Flexiheat UK

Option 2

Our “MV” or “MXV” range of buffer tanks is for both closed heating and cooling systems.

2000 Litre buffer vessel or tank MV mild steel or MXV stainless steel models from Flexiheat UK

MV or MXV buffer tanks

Both buffer tank options are rated to:

Maximum working pressure: 6 bar

Maximum working temperature: 110 ºC

The “MV” buffer tank range is manufactured in mild steel, while our “MVX” buffer tank range is manufactured in 304 stainless steel and offers higher durability and resistance to corrosion.

These tanks are thermally insulated with rigid, mould-injected (this system guarantees a perfectly regular insulation thickness with optimum material density), 80mm thick PU polyurethane foam insulation, with an insulation piece on the optional 400mm side manhole on the “IB” models. This thermal insulation is both CFC- and HCFC-free and fire-resistance class B-s2do according to EN 13501.

The products are ERP-compliant, offers a “C” rating as standard (EU 812/2013), and come with three years warranty.

Technical data for MV and MXV units

Both buffer tank options come with four x 4″ female BSP tappings (designated “S” on the above drawing) and various other tappings for temperature probes or sensors, temperature gauges, or working pressure sensors or gauges to be fitted to the tank.

Technical detail of our 2000 Litre buffer tanks or vessels in mild steel or stainless steel 304 from Flexiheat UK

“I” model – no clean out port – “IB” with 400mm clean out port

The buffer tank can optionally be supplied with a “UV” restitant PVC-padded external lining or “ALUNOX” aluminium sheet covering for external use. This is typically required or standard in coastal areas of the UK to prevent seagulls from pecking at the buffer tank’s insulation.

Each buffer tank option comes with a tapping for a backup electric immersion heater to be fitted to the tank if so required.

2000IB - 2000 Litre buffer tank with inspection and maintenance manhole in carbon steel or stainless steel from Flexiheat UK

IB Version – with inspection and maintenance manhole.

IB MODELS: A side 400mm manhole provides access to the inside buffer tank for tasks such as inspection, cleaning, and maintenance.

These buffer tanks are detailed on page 11 of the following brochure:

Download the Buffer tanks for thermal storage for heating or chilled water in HVAC systems brochure from Flexiheat UK

Heat Exchanger Coil Options

We also do a range of buffer tanks that have an intermediate coil or coils within the tank to hydraulically separate the heating or cooling source from the water in the buffer tank. You can think of these as large “low loss headers” or an indirect water heater which offers the guarantee that any heating system sludge from an existing system is prevented from entering the heat pumps, biomass boilers, solar, or geothermal systems.For further information on this range of buffer tanks please see here: Buffer tank with coil or twin coils

Please note that these are not domestic hot water cylinders for the production of domestic hot water for commercial water heating; we supply these water heaters or calorifiers, and these are listed on this webpage: commercial domestic hot water calorifiers

System requirements and compatibility: ensuring the right fit

The system requirements and compatibility of the buffer tank should be considered, including the working pressure, insulation,insulation and tappings.

These buffer tanks are ideal for the specific application, whether it’s for biomass, air source heat pump, ground source heat pumps and gas, wood pellet, gasification, or oil boilers.

The budget and cost of the buffer tank should be considered, including the price of the tank and any additional features required.

Regular maintenance and upkeep of the buffer tank

Regular maintenance and upkeep are essential to ensure the longevity of the buffer tank. Tips for maintenance include checking the tank’s insulation and working pressure.

Contact us

At Flexiheat UK, our technical sales staff are available to provide support, further information, or to place an order for our 2000 Litre buffer tank or vessel options for hvac systems. Speak to us on 01202 822221 from Monday to Friday, 9 a.m. to 5 p.m., or email us via our Contact Page.